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128-450: The geography of Iowa includes the study of bedrock, landforms, rivers, geology, paleontology and urbanisation of the U.S. state of Iowa . The state covers an area of 56,272.81 sq mi (145,746 km). Iowa's bedrock geology generally increases in age from west to east. In northwest Iowa Cretaceous bedrock is ca. 74 million years old; in eastern Iowa Cambrian bedrock dates to ca. 500 million years ago. Seventy-four million years ago,
256-455: A Mohs hardness of 2 to 4, dense limestone can have a crushing strength of up to 180 MPa . For comparison, concrete typically has a crushing strength of about 40 MPa. Although limestones show little variability in mineral composition, they show great diversity in texture. However, most limestone consists of sand-sized grains in a carbonate mud matrix. Because limestones are often of biological origin and are usually composed of sediment that
384-457: A bloom of cyanobacteria or microalgae . However, stable isotope ratios in modern carbonate mud appear to be inconsistent with either of these mechanisms, and abrasion of carbonate grains in high-energy environments has been put forward as a third possibility. Formation of limestone has likely been dominated by biological processes throughout the Phanerozoic , the last 540 million years of
512-434: A carbonate rock outcrop can be estimated in the field by etching the surface with dilute hydrochloric acid. This etches away the calcite and aragonite, leaving behind any silica or dolomite grains. The latter can be identified by their rhombohedral shape. Crystals of calcite, quartz , dolomite or barite may line small cavities ( vugs ) in the rock. Vugs are a form of secondary porosity, formed in existing limestone by
640-612: A central quartz grain or carbonate mineral fragment. These likely form by direct precipitation of calcium carbonate onto the ooid. Pisoliths are similar to ooids, but they are larger than 2 mm in diameter and tend to be more irregular in shape. Limestone composed mostly of ooids is called an oolite or sometimes an oolitic limestone . Ooids form in high-energy environments, such as the Bahama platform, and oolites typically show crossbedding and other features associated with deposition in strong currents. Oncoliths resemble ooids but show
768-449: A change in environment that increases the solubility of calcite. Dense, massive limestone is sometimes described as "marble". For example, the famous Portoro "marble" of Italy is actually a dense black limestone. True marble is produced by recrystallization of limestone during regional metamorphism that accompanies the mountain building process ( orogeny ). It is distinguished from dense limestone by its coarse crystalline texture and
896-949: A composition reflecting the organisms that produced them and the environment in which they were produced. Low-magnesium calcite skeletal grains are typical of articulate brachiopods , planktonic (free-floating) foraminifera, and coccoliths . High-magnesium calcite skeletal grains are typical of benthic (bottom-dwelling) foraminifera, echinoderms , and coralline algae . Aragonite skeletal grains are typical of molluscs , calcareous green algae , stromatoporoids , corals , and tube worms . The skeletal grains also reflect specific geological periods and environments. For example, coral grains are more common in high-energy environments (characterized by strong currents and turbulence) while bryozoan grains are more common in low-energy environments (characterized by quiet water). Ooids (sometimes called ooliths) are sand-sized grains (less than 2mm in diameter) consisting of one or more layers of calcite or aragonite around
1024-412: A considerable fraction of the limestone bed. At depths greater than 1 km (0.62 miles), burial cementation completes the lithification process. Burial cementation does not produce stylolites. When overlying beds are eroded, bringing limestone closer to the surface, the final stage of diagenesis takes place. This produces secondary porosity as some of the cement is dissolved by rainwater infiltrating
1152-463: A decline in air quality. Other factors negatively affecting Iowa's environment include the extensive use of older coal-fired power plants , fertilizer and pesticide runoff from crop production, and diminishment of the Jordan Aquifer . The 2020–2023 North American drought has affected Iowa particularly: As of January 2024, Iowa was in its 187th consecutive week of at least moderate drought ,
1280-483: A drop of dilute hydrochloric acid is dropped on it. Dolomite is also soft but reacts only feebly with dilute hydrochloric acid, and it usually weathers to a characteristic dull yellow-brown color due to the presence of ferrous iron. This is released and oxidized as the dolomite weathers. Impurities (such as clay , sand, organic remains, iron oxide , and other materials) will cause limestones to exhibit different colors, especially with weathered surfaces. The makeup of
1408-621: A few million years, as this is the most stable form of calcium carbonate. Ancient carbonate formations of the Precambrian and Paleozoic contain abundant dolomite, but limestone dominates the carbonate beds of the Mesozoic and Cenozoic . Modern dolomite is quite rare. There is evidence that, while the modern ocean favors precipitation of aragonite, the oceans of the Paleozoic and middle to late Cenozoic favored precipitation of calcite. This may indicate
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#17328449722731536-455: A few thousand years. As rainwater mixes with groundwater, aragonite and high-magnesium calcite are converted to low-calcium calcite. Cementing of thick carbonate deposits by rainwater may commence even before the retreat of the sea, as rainwater can infiltrate over 100 km (60 miles) into sediments beneath the continental shelf. As carbonate sediments are increasingly deeply buried under younger sediments, chemical and mechanical compaction of
1664-490: A high percentage of the mineral dolomite , CaMg(CO 3 ) 2 . Magnesian limestone is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite ( dolomitic limestone ), or for any other limestone containing a significant percentage of magnesium . Most limestone was formed in shallow marine environments, such as continental shelves or platforms , though smaller amounts were formed in many other environments. Much dolomite
1792-456: A large asteroid crashed into what is now southeast Pocahontas county creating the Manson crater . Nearly 22 miles in diameter, it would have killed most animals within 650 miles, roughly an area from modern Denver to Detroit. This was originally thought to have been one of the causes of the dinosaur extinction, but recalculation of the impact's age indicates it occurred some 12 million years before
1920-435: A limestone sample except in thin section and are less common in ancient limestones, possibly because compaction of carbonate sediments disrupts them. Limeclasts are fragments of existing limestone or partially lithified carbonate sediments. Intraclasts are limeclasts that originate close to where they are deposited in limestone, while extraclasts come from outside the depositional area. Intraclasts include grapestone , which
2048-466: A lower Mg/Ca ratio in the ocean water of those times. This magnesium depletion may be a consequence of more rapid sea floor spreading , which removes magnesium from ocean water. The modern ocean and the ocean of the Mesozoic have been described as "aragonite seas". Most limestone was formed in shallow marine environments, such as continental shelves or platforms . Such environments form only about 5% of
2176-525: A lower diversity of organisms and a greater fraction of silica and clay minerals characteristic of marls . The Green River Formation is an example of a prominent freshwater sedimentary formation containing numerous limestone beds. Freshwater limestone is typically micritic. Fossils of charophyte (stonewort), a form of freshwater green algae, are characteristic of these environments, where the charophytes produce and trap carbonates. Limestones may also form in evaporite depositional environments . Calcite
2304-523: A mechanism for dolomitization, with one 2004 review paper describing it bluntly as "a myth". Ordinary seawater is capable of converting calcite to dolomite, if the seawater is regularly flushed through the rock, as by the ebb and flow of tides (tidal pumping). Once dolomitization begins, it proceeds rapidly, so that there is very little carbonate rock containing mixed calcite and dolomite. Carbonate rock tends to be either almost all calcite/aragonite or almost all dolomite. About 20% to 25% of sedimentary rock
2432-448: A plausible source of mud. Another possibility is direct precipitation from the water. A phenomenon known as whitings occurs in shallow waters, in which white streaks containing dispersed micrite appear on the surface of the water. It is uncertain whether this is freshly precipitated aragonite or simply material stirred up from the bottom, but there is some evidence that whitings are caused by biological precipitation of aragonite as part of
2560-514: A proposed Ordovician meteor event . Buried deeply within Iowa's bedrock, the Midcontinent Rift System can be seen clearly in magnetic anomaly maps of Iowa. This is a billion-year-old tectonic plate scar that extends from Kansas through Lake Superior . This rift is not seismically active. No major active fault lines exist in Iowa, and Iowa is one of the most seismically stable states in
2688-449: A radial rather than layered internal structure, indicating that they were formed by algae in a normal marine environment. Peloids are structureless grains of microcrystalline carbonate likely produced by a variety of processes. Many are thought to be fecal pellets produced by marine organisms. Others may be produced by endolithic (boring) algae or other microorganisms or through breakdown of mollusc shells. They are difficult to see in
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#17328449722732816-403: A strong smell, and the limestone bedrock in much of the state causes hard water. Some communities, such as Iowa City resort to additional carbon filtration and lime softening coagulation-sedimentation to make the water more palatable. Water treatment can be surprisingly effective; Des Moines' advanced filtration system has led to water quality ranked among the nation's best. The Jordan Aquifer
2944-603: A visitors' center, where hikers can tour the bedrock. Unfortunately, looters have illegally removed many of the better fossils. The June 2008 floods expanded the fossil bed floor, and removed some of the weathered overburden. Jurassic and Cretaceous bedrock in western Iowa have potential to contain dinosaur remains, and in nearby parts of Nebraska Hadrosaurid (“duck-billed”) ornithopod dinosaur remains have been recovered in Cretaceous bedrock similar to that of Iowa. The deep loess that covers much of western Iowa typically conceals
3072-543: Is 47. In 2008 , twelve people were killed by tornadoes in Iowa, making it the deadliest year since 1968 and also the second most tornadoes in a year with 105, matching the total from 2001. Iowa summers are known for heat and humidity, with daytime temperatures sometimes near 90 °F (32 °C) and occasionally exceeding 100 °F (38 °C). Average winters in the state have been known to drop well below freezing, even dropping below −18 °F (−28 °C). Iowa's all-time hottest temperature of 118 °F (48 °C)
3200-595: Is a line along 43 degrees, 30 minutes north latitude. The southern border is the Des Moines River and a not-quite-straight line along approximately 40 degrees 35 minutes north, as decided by the U.S. Supreme Court in Missouri v. Iowa (1849) after a standoff between Missouri and Iowa known as the Honey War . Iowa is the only state whose east and west borders are formed almost entirely by rivers. Carter Lake, Iowa ,
3328-416: Is a type of carbonate sedimentary rock which is the main source of the material lime . It is composed mostly of the minerals calcite and aragonite , which are different crystal forms of CaCO 3 . Limestone forms when these minerals precipitate out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as
3456-560: Is also favored on the seaward margin of shelves and platforms, where there is upwelling deep ocean water rich in nutrients that increase organic productivity. Reefs are common here, but when lacking, ooid shoals are found instead. Finer sediments are deposited close to shore. The lack of deep sea limestones is due in part to rapid subduction of oceanic crust, but is more a result of dissolution of calcium carbonate at depth. The solubility of calcium carbonate increases with pressure and even more with higher concentrations of carbon dioxide, which
3584-482: Is an uncommon mineral in limestone, and siderite or other carbonate minerals are rare. However, the calcite in limestone often contains a few percent of magnesium . Calcite in limestone is divided into low-magnesium and high-magnesium calcite, with the dividing line placed at a composition of 4% magnesium. High-magnesium calcite retains the calcite mineral structure, which is distinct from dolomite. Aragonite does not usually contain significant magnesium. Most limestone
3712-402: Is carbonate rock, and most of this is limestone. Limestone is found in sedimentary sequences as old as 2.7 billion years. However, the compositions of carbonate rocks show an uneven distribution in time in the geologic record. About 95% of modern carbonates are composed of high-magnesium calcite and aragonite. The aragonite needles in carbonate mud are converted to low-magnesium calcite within
3840-574: Is categorized as the Central forest-grasslands transition ecoregion. The Northern, drier part of Iowa is categorized as part of the Central tall grasslands . There is a dearth of natural areas in Iowa; less than 1% of the tallgrass prairie that once covered most of Iowa remains intact; only about 5% of the state's prairie pothole wetlands remain, and most of the original forest has been lost. As of 2005 Iowa ranked 49th of U.S. states in public land holdings. Threatened or endangered animals in Iowa include
3968-474: Is clusters of peloids cemented together by organic material or mineral cement. Extraclasts are uncommon, are usually accompanied by other clastic sediments, and indicate deposition in a tectonically active area or as part of a turbidity current . The grains of most limestones are embedded in a matrix of carbonate mud. This is typically the largest fraction of an ancient carbonate rock. Mud consisting of individual crystals less than 5 μm (0.20 mils) in length
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4096-416: Is commonly white to gray in color. Limestone that is unusually rich in organic matter can be almost black in color, while traces of iron or manganese can give limestone an off-white to yellow to red color. The density of limestone depends on its porosity, which varies from 0.1% for the densest limestone to 40% for chalk. The density correspondingly ranges from 1.5 to 2.7 g/cm . Although relatively soft, with
4224-420: Is controlled largely by the amount of dissolved carbon dioxide ( CO 2 ) in the water. This is summarized in the reaction: Increases in temperature or decreases in pressure tend to reduce the amount of dissolved CO 2 and precipitate CaCO 3 . Reduction in salinity also reduces the solubility of CaCO 3 , by several orders of magnitude for fresh water versus seawater. Near-surface water of
4352-545: Is converted to low-magnesium calcite. Diagenesis is the likely origin of pisoliths , concentrically layered particles ranging from 1 to 10 mm (0.039 to 0.394 inches) in diameter found in some limestones. Pisoliths superficially resemble ooids but have no nucleus of foreign matter, fit together tightly, and show other signs that they formed after the original deposition of the sediments. Silicification occurs early in diagenesis, at low pH and temperature, and contributes to fossil preservation. Silicification takes place through
4480-503: Is deposited close to where it formed, classification of limestone is usually based on its grain type and mud content. Most grains in limestone are skeletal fragments of marine organisms such as coral or foraminifera . These organisms secrete structures made of aragonite or calcite, and leave these structures behind when they die. Other carbonate grains composing limestones are ooids , peloids , and limeclasts ( intraclasts and extraclasts [ ca ] ). Skeletal grains have
4608-460: Is described as coquinite . Chalk is a soft, earthy, fine-textured limestone composed of the tests of planktonic microorganisms such as foraminifera, while marl is an earthy mixture of carbonates and silicate sediments. Limestone forms when calcite or aragonite precipitate out of water containing dissolved calcium, which can take place through both biological and nonbiological processes. The solubility of calcium carbonate ( CaCO 3 )
4736-617: Is described as micrite . In fresh carbonate mud, micrite is mostly small aragonite needles, which may precipitate directly from seawater, be secreted by algae, or be produced by abrasion of carbonate grains in a high-energy environment. This is converted to calcite within a few million years of deposition. Further recrystallization of micrite produces microspar , with grains from 5 to 15 μm (0.20 to 0.59 mils) in diameter. Limestone often contains larger crystals of calcite, ranging in size from 0.02 to 0.1 mm (0.79 to 3.94 mils), that are described as sparry calcite or sparite . Sparite
4864-462: Is distinguished from micrite by a grain size of over 20 μm (0.79 mils) and because sparite stands out under a hand lens or in thin section as white or transparent crystals. Sparite is distinguished from carbonate grains by its lack of internal structure and its characteristic crystal shapes. Geologists are careful to distinguish between sparite deposited as cement and sparite formed by recrystallization of micrite or carbonate grains. Sparite cement
4992-465: Is marked by rolling terrain and ridges. Historically, this area was peppered with small interconnected swamps, most of which were drained for farmland. The Iowa Great Lakes occur along the western edge of the Des Moines lobe. The southern Iowa drift plain covers most of the southern half of Iowa. This is probably the most familiar landscape to travelers, since most of Interstate 80 in Iowa runs through
5120-560: Is one of the first minerals to precipitate in marine evaporites. Most limestone is formed by the activities of living organisms near reefs, but the organisms responsible for reef formation have changed over geologic time. For example, stromatolites are mound-shaped structures in ancient limestones, interpreted as colonies of cyanobacteria that accumulated carbonate sediments, but stromatolites are rare in younger limestones. Organisms precipitate limestone both directly as part of their skeletons, and indirectly by removing carbon dioxide from
5248-473: Is otherwise chemically fairly pure, with clastic sediments (mainly fine-grained quartz and clay minerals ) making up less than 5% to 10% of the composition. Organic matter typically makes up around 0.2% of a limestone and rarely exceeds 1%. Limestone often contains variable amounts of silica in the form of chert or siliceous skeletal fragments (such as sponge spicules, diatoms , or radiolarians ). Fossils are also common in limestone. Limestone
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5376-520: Is part of the Driftless Area , consisting of steep hills and valleys which appear as mountainous. Several natural lakes exist, most notably Spirit Lake , West Okoboji Lake , and East Okoboji Lake in northwest Iowa ( see Iowa Great Lakes ). To the east lies Clear Lake . Man-made lakes include Lake Odessa, Saylorville Lake , Lake Red Rock , Coralville Lake , Lake MacBride, and Rathbun Lake. Before European settlement, 4 to 6 million acres of
5504-472: Is produced by decaying organic matter settling into the deep ocean that is not removed by photosynthesis in the dark depths. As a result, there is a fairly sharp transition from water saturated with calcium carbonate to water unsaturated with calcium carbonate, the lysocline , which occurs at the calcite compensation depth of 4,000 to 7,000 m (13,000 to 23,000 feet). Below this depth, foraminifera tests and other skeletal particles rapidly dissolve, and
5632-462: Is ranked among the best states and it performs highly on metrics such as governance, education, infrastructure, and safety. Like many other states , Iowa takes its name from its predecessor, Iowa Territory , whose name in turn is derived from the Iowa River , and ultimately from the ethnonym of the indigenous Ioway people . The Ioway are a Chiwere -speaking Siouan Nation , who were once part of
5760-417: Is seasonal, with more rain falling in the summer months. Virtually statewide, the driest month is January or February, and the wettest month is June, owing to frequent showers and thunderstorms, some of which produce hail, damaging winds and/or tornadoes. In Des Moines, roughly in the center of the state, over two-thirds of the 34.72 inches (88.2 cm) of rain falls from April through September, and about half
5888-514: Is secondary dolomite, formed by chemical alteration of limestone. Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly soluble in rainwater, these exposures often are eroded to become karst landscapes. Most cave systems are found in limestone bedrock. Limestone has numerous uses: as a chemical feedstock for the production of lime used for cement (an essential component of concrete ), as aggregate for
6016-487: Is the brain drain , in which educated young adults leave the state in search of better prospects in higher education or employment. During the 1990s, Iowa had the second highest exodus rate for single, educated young adults, second only to North Dakota. The United States Census Bureau determined the population of Iowa was 3,190,369 on April 1, 2020, a 4.73% increase since the 2010 United States census . Limestone Limestone ( calcium carbonate CaCO 3 )
6144-413: Is the largest source of groundwater, extending from northeast Iowa to south central Iowa, and is ultimately the source of much of Iowa's agricultural and industrial water. In addition to pollution threats, the aquifer is threatened by overuse in well-source irrigation, ethanol production, and the diminishment of resupply caused by extensive field tilling. The aquifer has dropped by as much as 300 feet since
6272-575: Is the only city in the state located west of the Missouri River. Iowa has 99 counties , but 100 county seats because Lee County has two. The state capital, Des Moines , is in Polk County . Iowa's bedrock geology generally decreases in age from east to west. In northwest Iowa, Cretaceous bedrock can be 74 million years old; in eastern Iowa Cambrian bedrock dates to c. 500 million years ago. The oldest radiometrically dated bedrock in
6400-631: The 1900 census , though Iowa now has a predominantly urban population. The Iowa Economic Development Authority, created in 2011 has replaced the Iowa Department of Economic Development and its annual reports are a source of economic information. Iowa is bordered by the Mississippi River on the east along with the Missouri River and the Big Sioux River on the west. The northern boundary
6528-529: The Cherokee Sewer Site . A Pleistocene giant sloth is under excavation along West Tarkio Creek near Shenandoah, Iowa . Three individuals of Megalonyx jeffersonii , or Jefferson's Ground Sloth, have been identified so far, including one adult and two juveniles of different ages. Samuel Calvin (1840–1911) was Iowa's first systematic geologist, who helped to make the first bedrock and landform maps of Iowa, as well as lead geological research throughout
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#17328449722736656-589: The Driftless Area , this region of scenic, high relief landscapes includes such features as resistant, bluff-forming bedrock outcrops , deep V-shaped valleys, caves, springs, and sinkholes . Glacial deposits and loess are thin or absent over most of the region. Often called the Prairie Pothole Region , the Des Moines Lobe was glaciated up until 12,000 years ago during the Wisconsin glaciation . The area
6784-584: The French and Indian War , transferred ownership to their ally, Spain. Spain practiced very loose control over the Iowa region, granting trading licenses to French and British traders, who established trading posts along the Mississippi and Des Moines Rivers . Iowa was part of a territory known as La Louisiane or Louisiana , and European traders were interested in lead and furs obtained by Indigenous people. The Sauk and Meskwaki effectively controlled trade on
6912-551: The Ho-Chunk Confederation that inhabited the area now corresponding to several Midwest states. The Ioway were one of the many Native American nations whose territory comprised the future state of Iowa before the time of European colonization. When Indigenous peoples of the Americas first arrived in what is now Iowa more than 13,000 years ago, they were hunters and gatherers living in a Pleistocene glacial landscape. By
7040-808: The Indiana Territory ) that surrendered much of Illinois to the U.S. enraged many Sauk and led to the 1832 Black Hawk War . The Sauk and Meskwaki were forced to sell some of their land in the Mississippi Valley to the U.S. in 1832 in the Black Hawk Purchase Treaty and sold their remaining land in Iowa in 1842, most of them moving to a reservation in Kansas. In 1837, some the Potawatomi from Illinois were resettled in Iowa, while many Meskwaki later returned to Iowa and settled near Tama, Iowa ;
7168-577: The Late Archaic period , Native Americans in Iowa began utilizing domesticated plants. The subsequent Woodland period saw an increased reliance on agriculture and social complexity, with increased use of mounds, ceramics, and specialized subsistence. During the Late Prehistoric period (beginning about AD 900) increased use of maize and social changes led to social flourishing and nucleated settlements. The arrival of European trade goods and diseases in
7296-760: The Meskwaki Settlement remains to this day. In 1856 the Iowa Legislature passed an unprecedented act allowing the Meskwaki to purchase the land. However, in contrast to the unprecedented act of the Iowa Legislature, the United States Federal Government, through the use of Treaties, forced the Ho-Chunk from Iowa in 1848, and forced the Dakota from Iowa by 1858. Western Iowa around modern Council Bluffs
7424-427: The Mississippi River , averages 52 °F (11 °C). Snowfall is common, with Des Moines getting about 26 days of snowfall a year, and other places, such as Shenandoah getting about 11 days of snowfall in a year. Spring ushers in the beginning of the severe weather season. As of 2008, Iowa averaged about 50 days of thunderstorm activity per year. As of 2015, the 30-year annual average of tornadoes in Iowa
7552-400: The Mississippi River , averages 52 °F (11 °C). Snowfall is common, with Des Moines getting about 26 days of snowfall a year, and other places, such as Shenandoah getting about 11 days of snowfall in a year. Spring ushers in the beginning of the severe weather season. Iowa averages about 50 days of thunderstorm activity per year. The 30-year annual average of tornadoes in Iowa
7680-587: The U.S. Congress established the Territory of Iowa . President Martin Van Buren appointed Robert Lucas governor of the territory, which at the time had 22 counties and a population of 23,242. Almost immediately after achieving territorial status, a clamor arose for statehood. On December 28, 1846, Iowa became the 29th state in the Union when President James K. Polk signed Iowa's admission bill into law. Once admitted to
7808-629: The War of 1812 , and Fort Shelby in Prairie du Chien, Wisconsin , also fell to the British. Black Hawk took part in the siege of Fort Madison. Another small military outpost was established along the Mississippi River in present-day Bellevue . This poorly situated stockade was similarly attacked by hundreds of Indigenous people in 1813, but was successfully defended and later abandoned until settlers returned to
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#17328449722737936-584: The interior least tern , piping plover , Indiana bat , pallid sturgeon , the Iowa Pleistocene land snail , Higgins' eye pearly mussel , and the Topeka shiner . Endangered or threatened plants include western prairie fringed orchid , eastern prairie fringed orchid , Mead's milkweed , prairie bush clover , and northern wild monkshood . The explosion in the number of high-density livestock facilities in Iowa has led to increased rural water contamination and
8064-436: The 19th century, resulting in dry wells, the disappearance of natural surface springs, and the diminishment of water quality. The NRCS divides Iowa into 23 soil regions. In general, soils of southern, eastern, and western Iowa are loess-derived, while soils of northern and central Iowa are till-derived. Most level areas of Iowa have soils highly suitable for agriculture, making Iowa one of the most productive farming regions of
8192-765: The Army of the Potomac in Virginia and fought under Union General Philip Sheridan in the Shenandoah Valley . Many died and were buried at Andersonville. They marched on General Nathaniel Banks ' ill-starred expedition to the Red River. Twenty-seven Iowans have been awarded the Medal of Honor , the highest military decoration awarded by the United States government, which was first awarded in
8320-503: The Civil War. Iowa had several brigadier generals and four major generals— Grenville Mellen Dodge , Samuel R. Curtis , Francis J. Herron , and Frederick Steele —and saw many of its generals go on to state and national prominence following the war. Following the Civil War, Iowa's population continued to grow dramatically, from 674,913 people in 1860 to 1,624,615 in 1880. The American Civil War briefly brought higher profits. In 1917,
8448-470: The Depression. The crisis spurred a major, decade-long population decline. After bottoming out in the 1980s, Iowa's economy began to reduce its dependence on agriculture. By the early 21st century, it was characterized by a mix of manufacturing, biotechnology, finance and insurance services, and government services. The population of Iowa has increased at a slower rate than the U.S. as a whole since at least
8576-496: The Earth's history. Limestone may have been deposited by microorganisms in the Precambrian , prior to 540 million years ago, but inorganic processes were probably more important and likely took place in an ocean more highly oversaturated in calcium carbonate than the modern ocean. Diagenesis is the process in which sediments are compacted and turned into solid rock . During diagenesis of carbonate sediments, significant chemical and textural changes take place. For example, aragonite
8704-510: The Indochina War. An exception was required for this resettlement as State Dept policy at the time forbid resettlement of large groups of refugees in concentrated communities; an exception was ultimately granted and 1200 Tai Dam were resettled in Iowa. Since then Iowa has accepted thousands of refugees from Laos, Cambodia, Thailand, Bhutan, and Burma. The farm crisis of the 1980s caused a major recession in Iowa, causing poverty not seen since
8832-556: The Iowa portion of the Quad Cities . Iowa is home to 940 small towns, though its population is increasingly urbanized as small communities and rural areas decline in population. During the 18th and early 19th centuries, Iowa was a part of French Louisiana and Spanish Louisiana ; its state flag is patterned after the flag of France . After the Louisiana Purchase , pioneers laid the foundation for an agriculture-based economy in
8960-572: The Louisiana Purchase into two parts—the Territory of Orleans and the District of Louisiana, with present-day Iowa falling in the latter. The Indiana Territory , created in 1800, exercised jurisdiction over this portion of the District; William Henry Harrison was its first governor. Much of Iowa was mapped by Zebulon Pike in 1805, but it was not until the construction of Fort Madison in 1808 that
9088-464: The Mississippi in the late 18th century and early 19th century. Among the early traders on the Mississippi were Julien Dubuque , Robert de la Salle , and Paul Marin . Along the Missouri River at least five French and English trading houses were built before 1808. In 1800, Napoleon Bonaparte took control of Louisiana from Spain in a treaty . After the 1803 Louisiana Purchase , Congress divided
9216-547: The Northwest Iowa Plains are rolling hills consisting of eroded soils developed since pre-Wisconsinan glaciation, but with significant amounts of loess. Perhaps the only truly flat region of Iowa, the Missouri Alluvial Plain contains areas of terraces, sloughs, and oxbows. Its valley trench is not as deep as the Mississippi River system, and the Missouri River is contained in a much narrower channel. In Iowa,
9344-476: The Protohistoric period led to dramatic population shifts and economic and social upheaval, with the arrival of new tribes and early European explorers and traders. There were numerous native American tribes living in Iowa at the time of early European exploration. Tribes which were probably descendants of the prehistoric Oneota include the Dakota , Ho-Chunk , Ioway , and Otoe . Tribes which arrived in Iowa in
9472-532: The SIDP. The classic Iowa landscape, consisting of rolling hills of Wisconsin-age loess on Illinoian (or earlier) till . The SIDP is some of the most productive agricultural land in the US. Generally level areas of stream terraces, paleochannels, backwater sloughs, and oxbow lakes are found within the broad Mississippi River valley. The Loess Hills consist of very thick deposits of loess in far western Iowa deposited during
9600-763: The U.S. With the exception of the 1968 Illinois earthquake which caused the water tower at Lineville to leak, no injuries or significant damage has ever been caused by earthquakes in Iowa. Occasional small earthquakes occur near Fremont County in the far southwest, and the Sioux City area can occasionally be shaken by nearby tremblors. Large earthquakes associated with the New Madrid Fault of far southern Illinois and Missouri can occasionally be felt in eastern Iowa. Recent earthquakes centered in Oklahoma have also been felt in Iowa, but have caused no damage. Historically, Iowa
9728-506: The U.S. established tenuous military control over the region. Fort Madison was built to control trade and establish U.S. dominance over the Upper Mississippi, but it was poorly designed and disliked by the Sauk and Meskwaki, many of whom allied with the British, who had not abandoned claims to the territory. Fort Madison was defeated by British-supported Indigenous people in 1813 during
9856-403: The Union, the state's boundary issues resolved, and most of its land purchased from Natives, Iowa set its direction to development and organized campaigns for settlers and investors, boasting the young frontier state's rich farmlands, fine citizens, free and open society, and good government. Iowa has a long tradition of state and county fairs. The first and second Iowa State Fairs were held in
9984-455: The United States entered World War I and farmers as well as all Iowans experienced a wartime economy. For farmers, the change was significant. Since the beginning of the war in 1914, Iowa farmers had experienced economic prosperity, which lasted until the end of the war. In the economic sector, Iowa also has undergone considerable change. Beginning with the first industries developed in the 1830s, which were mainly for processing materials grown in
10112-521: The Wisconsin and Illinoian periods. Highly eroded, leaving stark, beautiful "golden hills". Northeast Iowa is covered with eroded Pre-Illinoian till with moderate loess formation, frequently in the form of paha ridges , muted relief except for steep rolling hills near river valleys, and deeper valleys. These picturesque hills are depicted in many of the landscapes of Grant Wood . Like the Iowan Surface,
10240-430: The accumulation of corals and shells in the sea, have likely been more important for the last 540 million years. Limestone often contains fossils which provide scientists with information on ancient environments and on the evolution of life. About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone. The remaining carbonate rock is mostly dolomite , a closely related rock, which contains
10368-513: The area in the mid-1830s. After the war, the U.S. re-established control of the region through the construction of Fort Armstrong , Fort Snelling in Minnesota , and Fort Atkinson in Nebraska . The United States encouraged settlement of the east side of the Mississippi and removal of Indians to the west. A disputed 1804 treaty between Quashquame and William Henry Harrison (then governor of
10496-550: The area, Iowa has experienced a gradual increase in the number of business and manufacturing operations. The transition from an agricultural economy to a mixed economy happened slowly. The Great Depression and World War II accelerated the shift away from smallholder farming to larger farms, and began a trend of urbanization. The period after World War II witnessed a particular increase in manufacturing operations. In 1975, Governor Robert D. Ray petitioned President Ford to allow Iowa to accept and resettle Tai Dam refugees fleeing
10624-628: The armed forces, over one-sixth of whom were killed before the Confederates surrendered at Appomattox . Most fought in the great campaigns in the Mississippi Valley and in the South . Iowa troops fought at Wilson's Creek in Missouri , Pea Ridge in Arkansas , Forts Henry and Donelson, Shiloh, Chattanooga, Chickamauga, Missionary Ridge, and Rossville Gap as well as Vicksburg, Iuka, and Corinth. They served with
10752-561: The average annual precipitation falls from May through August, peaking in June. As in most of the U.S., surface water in Iowa is never safe to drink untreated, contamination by agricultural runoff including nitrates , herbicides , pesticides , and animal waste is common, though the Clean Water Act has helped. Municipal water supplies are typically heavily chlorinated, this chlorine, combined with high nitrate levels, often give municipal water
10880-434: The base of roads, as white pigment or filler in products such as toothpaste or paint, as a soil conditioner , and as a popular decorative addition to rock gardens . Limestone formations contain about 30% of the world's petroleum reservoirs . Limestone is composed mostly of the minerals calcite and aragonite , which are different crystal forms of calcium carbonate ( CaCO 3 ). Dolomite , CaMg(CO 3 ) 2 ,
11008-470: The bedrock, limiting opportunities to finding dinosaurs to mining and quarrying operations. Archaeological and paleontological sites in Iowa have produced an extensive collection of Pleistocene and Holocene animals; these have been used to reconstruct past environmental conditions in the Midwest. Some of the earliest paleoclimatic reconstructions of the midcontinent were made from Iowa collections, such as
11136-657: The beds. This may include the formation of vugs , which are crystal-lined cavities within the limestone. Diagenesis may include conversion of limestone to dolomite by magnesium-rich fluids. There is considerable evidence of replacement of limestone by dolomite, including sharp replacement boundaries that cut across bedding. The process of dolomitization remains an area of active research, but possible mechanisms include exposure to concentrated brines in hot environments ( evaporative reflux ) or exposure to diluted seawater in delta or estuary environments ( Dorag dolomitization ). However, Dorag dolomitization has fallen into disfavor as
11264-462: The depositional fabric of carbonate rocks. Dunham divides the rocks into four main groups based on relative proportions of coarser clastic particles, based on criteria such as whether the grains were originally in mutual contact, and therefore self-supporting, or whether the rock is characterized by the presence of frame builders and algal mats. Unlike the Folk scheme, Dunham deals with the original porosity of
11392-469: The deposits are highly porous, so that they have a spongelike texture, they are typically described as tufa . Secondary calcite deposited by supersaturated meteoric waters ( groundwater ) in caves is also sometimes described as travertine. This produces speleothems , such as stalagmites and stalactites . Coquina is a poorly consolidated limestone composed of abraded pieces of coral , shells , or other fossil debris. When better consolidated, it
11520-406: The earth's oceans are oversaturated with CaCO 3 by a factor of more than six. The failure of CaCO 3 to rapidly precipitate out of these waters is likely due to interference by dissolved magnesium ions with nucleation of calcite crystals, the necessary first step in precipitation. Precipitation of aragonite may be suppressed by the presence of naturally occurring organic phosphates in
11648-531: The eastern border of the Missouri Plains is the Loess Hills, forming steep rounded bluffs. Iowa has a humid continental climate throughout the state ( Köppen climate classification Dfa ) with extremes of both heat and cold. The average annual temperature at Des Moines is 50 °F (10 °C); for some locations in the north, such as Mason City, the figure is about 45 °F (7 °C), while Keokuk , on
11776-437: The expense of more rural counties. Iowa, in common with other Midwestern states (especially Kansas , Nebraska , North Dakota , and South Dakota ), is feeling the brunt of rural flight , although Iowa has been gaining population since approximately 1990. Some smaller communities, such as Denison and Storm Lake , have mitigated this population loss through gains in immigrant laborers. Another demographic problem for Iowa
11904-574: The fairgrounds were being used as an army supply depot; and in 2020 due to the COVID-19 pandemic in the United States . Iowa supported the Union during the Civil War , voting heavily for Abraham Lincoln , though there was an antiwar " Copperhead " movement in the state, caused partially by a drop in crop prices caused by the war. There were no battles in the state, although the Battle of Athens , Missouri, 1861,
12032-399: The first refers to the grains and the second to the cement. For example, a limestone consisting mainly of ooids, with a crystalline matrix, would be termed an oosparite. It is helpful to have a petrographic microscope when using the Folk scheme, because it is easier to determine the components present in each sample. Robert J. Dunham published his system for limestone in 1962. It focuses on
12160-572: The formation of distinctive minerals from the silica and clay present in the original limestone. Two major classification schemes, the Folk and Dunham, are used for identifying the types of carbonate rocks collectively known as limestone. Robert L. Folk developed a classification system that places primary emphasis on the detailed composition of grains and interstitial material in carbonate rocks . Based on composition, there are three main components: allochems (grains), matrix (mostly micrite), and cement (sparite). The Folk system uses two-part names;
12288-429: The geologic record are called bioherms . Many are rich in fossils, but most lack any connected organic framework like that seen in modern reefs. The fossil remains are present as separate fragments embedded in ample mud matrix. Much of the sedimentation shows indications of occurring in the intertidal or supratidal zones, suggesting sediments rapidly fill available accommodation space in the shelf or platform. Deposition
12416-706: The heart of the Corn Belt . In the latter half of the 20th century, Iowa's agricultural economy began to transition to a diversified economy of advanced manufacturing, processing, financial services , information technology , biotechnology , and green energy production. Politically, Iowa is notable for the Iowa Caucuses , an influential event in national politics, as well as its high levels of voter turnout and foundational leadership in civil rights including early adoption or support of black suffrage , women's rights , and same-sex marriage . Iowa's standard of living
12544-521: The impact, as the Winneshiek Shale is more than 50 feet below the bottom of the Upper Iowa River . The impact, equivalent to 1,000 megatons of TNT , did not appear to penetrate the Earth's mantle, but it did push down the underlying Ordovician and Cambrian bedrock several hundred feet. It may be one of several Middle Ordovician meteors that fell roughly simultaneously 469 million years ago, part of
12672-568: The last commercial mine closed in 1994. Iowa has very limited natural gas and oil production. Although Iowa's bedrock is generally younger in western parts of the state, one exception is a small part of far northwest Iowa where Precambrian Sioux quartzite bedrock is found in northwest Lyon County . Sioux quartzite is a very hard rock of ruddy pink color used extensively in the region for road and railroad beds. Sioux quartzite has been dated to have been laid between 1.64 and 1.76 billion years ago. Geodes are found in southeast Iowa and are
12800-488: The late prehistoric or protohistoric periods include the Illiniwek , Meskwaki , Omaha , and Sauk . The first known European explorers to document Iowa were Jacques Marquette and Louis Jolliet who traveled the Mississippi River in 1673 documenting several Indigenous villages on the Iowa side. The area of Iowa was claimed for France and remained a French territory until 1763. The French, before their impending defeat in
12928-403: The longest stretch since the 1950s. 96% of areas are affected by drought. Iowa has a humid continental climate throughout the state ( Köppen climate classification Dfa ) with extremes of both heat and cold. The average annual temperature at Des Moines is 50 °F (10 °C); for some locations in the north, such as Mason City, the figure is about 45 °F (7 °C), while Keokuk , on
13056-514: The mass extinction. Although glaciation has erased all surface evidence of the impact, the bedrock associated with this impact is unique in Iowa. A much older meteorite strike created the Decorah crater during the Middle Ordovician Period, 470 million years ago. The crater is estimated to be 3.5 miles (5.6 km) in diameter, covered by Winneshiek Shale. There is no surface evidence of
13184-590: The more developed eastern part of the state at Fairfield . The first fair was held October 25–27, 1854, at a cost of around $ 323. Thereafter, the fair moved to locations closer to the center of the state and in 1886 found a permanent home in Des Moines. The State Fair has been held annually since then, except for a few exceptions: 1898 due to the Spanish–American War and the World's Fair being held in nearby Omaha, Nebraska ; from 1942 to 1945, due to World War II , as
13312-402: The northwest of the state receiving less than 28 inches (71 cm). The pattern of precipitation across Iowa is seasonal with more rain falling in the summer months. Virtually statewide, the driest month is January or February, and the wettest month is June owing to frequent showers and thunderstorms some of which produce hail, damaging winds or tornadoes. In Des Moines, roughly in the center of
13440-410: The ocean basins, but limestone is rarely preserved in continental slope and deep sea environments. The best environments for deposition are warm waters, which have both a high organic productivity and increased saturation of calcium carbonate due to lower concentrations of dissolved carbon dioxide. Modern limestone deposits are almost always in areas with very little silica-rich sedimentation, reflected in
13568-497: The official state rock. They consist of grey to pink cobbles within limestone that when cut or smashed open reveal a hollow crystal-filled interior. Geodes are common around Geode State Park in Henry County . Despite popular perception, Iowa is generally not flat; most of the state consists of rolling hills. Prior divides Iowa into eight landforms based on glaciation , soils , topography , and river drainage: Also known as
13696-426: The reaction: Fossils are often preserved in exquisite detail as chert. Cementing takes place rapidly in carbonate sediments, typically within less than a million years of deposition. Some cementing occurs while the sediments are still under water, forming hardgrounds . Cementing accelerates after the retreat of the sea from the depositional environment, as rainwater infiltrates the sediment beds, often within just
13824-482: The relative purity of most limestones. Reef organisms are destroyed by muddy, brackish river water, and carbonate grains are ground down by much harder silicate grains. Unlike clastic sedimentary rock, limestone is produced almost entirely from sediments originating at or near the place of deposition. Limestone formations tend to show abrupt changes in thickness. Large moundlike features in a limestone formation are interpreted as ancient reefs , which when they appear in
13952-460: The rock. The Dunham scheme is more useful for hand samples because it is based on texture, not the grains in the sample. A revised classification was proposed by Wright (1992). It adds some diagenetic patterns to the classification scheme. Travertine is a term applied to calcium carbonate deposits formed in freshwater environments, particularly waterfalls , cascades and hot springs . Such deposits are typically massive, dense, and banded. When
14080-479: The sediments increases. Chemical compaction takes place by pressure solution of the sediments. This process dissolves minerals from points of contact between grains and redeposits it in pore space, reducing the porosity of the limestone from an initial high value of 40% to 80% to less than 10%. Pressure solution produces distinctive stylolites , irregular surfaces within the limestone at which silica-rich sediments accumulate. These may reflect dissolution and loss of
14208-662: The sediments of the ocean floor abruptly transition from carbonate ooze rich in foraminifera and coccolith remains ( Globigerina ooze) to silicic mud lacking carbonates. In rare cases, turbidites or other silica-rich sediments bury and preserve benthic (deep ocean) carbonate deposits. Ancient benthic limestones are microcrystalline and are identified by their tectonic setting. Fossils typically are foraminifera and coccoliths. No pre-Jurassic benthic limestones are known, probably because carbonate-shelled plankton had not yet evolved. Limestones also form in freshwater environments. These limestones are not unlike marine limestone, but have
14336-470: The state is the 2.9 billion year old Otter Creek Layered Mafic Complex. Precambrian rock is exposed only in the northwest of the state. Iowa can be divided into eight landforms based on glaciation , soils , topography , and river drainage. Loess hills lie along the western border of the state, some of which are several hundred feet thick. Northeast Iowa along the Upper Mississippi River
14464-532: The state was covered with wetlands, about 95% of these wetlands have been drained. Iowa's natural vegetation is tallgrass prairie and savanna in upland areas, with dense forest and wetlands in flood plains and protected river valleys, and pothole wetlands in northern prairie areas. Most of Iowa is used for agriculture; crops cover 60% of the state, grasslands (mostly pasture and hay with some prairie and wetland) cover 30%, and forests cover 7%; urban areas and water cover another 1% each. The southern part of Iowa
14592-583: The state, over two-thirds of the 34.72 inches (88.2 cm) of rain falls from April through September, and about half the average annual precipitation falls from May through August peaking in June. Iowa's population is more urban than rural, with 61 percent living in urban areas in 2000, a trend that began in the early 20th century. Urban counties in Iowa grew 8.5% from 2000 to 2008, while rural counties declined by 4.2%. The shift from rural to urban has caused population increases in more urbanized counties such as Dallas , Johnson , Linn , Polk , and Scott , at
14720-590: The state. Calvin Hall at the University of Iowa is named for him. Clair Cameron Patterson (1922–1995) developed the lead-lead dating and calculated an age for the Earth of 4.55 billion years; a figure far more accurate than those that existed at the time and one that has remained unchanged for over 50 years. Charles Rollin Keyes was also an early Iowa geologist who helped map the soils and bedrock of southeast Iowa; he, with Calvin,
14848-456: The time European explorers and traders visited Iowa, Native Americans were largely settled farmers with complex economic, social, and political systems. This transformation happened gradually. During the Archaic period (10,500 to 2,800 years ago), Native Americans adapted to local environments and ecosystems, slowly becoming more sedentary as populations increased. More than 3,000 years ago, during
14976-533: The water by photosynthesis and thereby decreasing the solubility of calcium carbonate. Limestone shows the same range of sedimentary structures found in other sedimentary rocks. However, finer structures, such as lamination , are often destroyed by the burrowing activities of organisms ( bioturbation ). Fine lamination is characteristic of limestone formed in playa lakes , which lack the burrowing organisms. Limestones also show distinctive features such as geopetal structures , which form when curved shells settle to
15104-553: The water. Although ooids likely form through purely inorganic processes, the bulk of CaCO 3 precipitation in the oceans is the result of biological activity. Much of this takes place on carbonate platforms . The origin of carbonate mud, and the processes by which it is converted to micrite, continue to be a subject of research. Modern carbonate mud is composed mostly of aragonite needles around 5 μm (0.20 mils) in length. Needles of this shape and composition are produced by calcareous algae such as Penicillus , making this
15232-582: The west, South Dakota to the northwest, and Minnesota to the north. Iowa is the 26th largest in total area and the 31st most populous of the 50 U.S. states , with a population of 3.19 million. The state's capital , most populous city , and largest metropolitan area fully located within the state is Des Moines . A portion of the larger Omaha, Nebraska, metropolitan area extends into three counties of southwest Iowa. Other metropolitan statistical areas in Iowa include Iowa City , Cedar Rapids , Waterloo-Cedar Falls , Ames , Dubuque , Sioux City , and
15360-549: The world. Like most Upper Midwest and Plains states, radon is a common problem in Iowa, especially in areas with clay-rich soils. Radon is the highest in the southern and the western parts of Iowa. Floods in 1993 washed away all the soil and unconsolidated bedrock along the spillway of the Coralville Lake Dam in Johnson County , exposing a rich collection of Devonian -age fossils . This area has been transformed into
15488-558: Was 47. In 2008 , twelve people were killed by tornadoes in Iowa, making it the deadliest year since 1968 and also the second most tornadoes in a year with 105, matching the total from 2001. Iowa summers are known for heat and humidity, with daytime temperatures sometimes near 90 °F (32 °C) and occasionally exceeding 100 °F (38 °C). Average winters in the state have been known to drop well below freezing, even dropping below −18 °F (−28 °C). As of 2018, Iowa's all-time hottest temperature of 118 °F (48 °C)
15616-537: Was a founder of the Iowa Geological Survey. Iowa Iowa ( / ˈ aɪ . ə w ə / EYE -ə-wə ) is a state in the upper Midwestern region of the United States . It borders the Mississippi River to the east and the Missouri River and Big Sioux River to the west; Wisconsin to the northeast, Illinois to the east and southeast, Missouri to the south, Nebraska to
15744-420: Was a significant coal producer, particularly the Des Moines River valley from Coalville south. Much of the greater City of Des Moines area was mined. Boone and What Cheer were important in the late 19th century. In the 20th century, the most important mines were farther south around Albia , Centerville , Lucas and Oskaloosa . Iowa coal tends to be too high in sulfur for modern applications, and
15872-590: Was fought just across the Des Moines River from Croton, Iowa , and shots from the battle landed in Iowa. Iowa sent large supplies of food to the armies and the eastern cities. Much of Iowa's support for the Union can be attributed to Samuel J. Kirkwood , its first wartime governor. Of a total population of 675,000, about 116,000 men were subjected to military duty. Iowa contributed proportionately more soldiers to Civil War military service than did any other state, north or south, sending more than 75,000 volunteers to
16000-416: Was likely deposited in pore space between grains, suggesting a high-energy depositional environment that removed carbonate mud. Recrystallized sparite is not diagnostic of depositional environment. Limestone outcrops are recognized in the field by their softness (calcite and aragonite both have a Mohs hardness of less than 4, well below common silicate minerals) and because limestone bubbles vigorously when
16128-457: Was recorded at Keokuk on July 20, 1934, during a nationwide heat wave; as of 2014, the all-time lowest temperature of −47 °F (−44 °C) was recorded in Washta on January 12, 1912. Iowa has had a relatively smooth gradient of varying precipitation across the state; from 1961 to 1990, areas in the southeast of the state received an average of over 38 inches (97 cm) of rain annually, and
16256-490: Was recorded at Keokuk on July 20, 1934, during a nationwide heat wave; the all-time lowest temperature of −47 °F (−44 °C) was recorded in Washta on January 12, 1912. Iowa has a relatively smooth gradient of varying precipitation across the state, with areas in the southeast of the state receiving an average of over 38 inches (97 cm) of rain annually, and the northwest of the state receiving less than 28 inches (71 cm). The pattern of precipitation across Iowa
16384-517: Was used as an Indian Reservation for members of the Council of Three Fires . The first American settlers officially moved to Iowa in June 1833. Primarily, they were families from Ohio , Pennsylvania , New York , Indiana , Kentucky , and Virginia who settled along the western banks of the Mississippi River , founding the modern day cities of Dubuque and Bellevue near the site of Julien Dubuque's 1785–1810 lead mining operation. On July 4, 1838,
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