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72-476: Outside Lands was the name used in the 19th century for the present-day Richmond District and Sunset District in San Francisco . With few roads and no public transportation, the area was covered by sand dunes and was considered inaccessible and uninhabitable. Today, after extensive development, the area consists of Golden Gate Park , Ocean Beach , and well-developed neighborhoods. Like all of California ,

144-605: A U.S. Army general, famous for his exploits during the Spanish–American War , the Philippine–American War , and the 1906 earthquake . Many of the east–west streets are still named after the Spanish Conquistadors , but there are exceptions. The creation of Golden Gate Park took out the streets previously lettered E through G. The former D Street became Fulton, which is the northern boundary of most of

216-555: A dune forms, plant succession occurs. The conditions on an embryo dune are harsh, with salt spray from the sea carried on strong winds. The dune is well drained and often dry, and composed of calcium carbonate from seashells. Rotting seaweed , brought in by storm waves adds nutrients to allow pioneer species to colonize the dune. For example, in the United Kingdom these pioneer species are often marram grass , sea wort grass and other sea grasses. These plants are well adapted to

288-590: A few tens of metres except at their nose, where vegetation stops or slows the advance of accumulating sand. Simple parabolic dunes have only one set of arms that trail upwind, behind the leading nose. Compound parabolic dunes are coalesced features with several sets of trailing arms. Complex parabolic dunes include subsidiary superposed or coalesced forms, usually of barchanoid or linear shapes. Parabolic dunes, like crescent dunes, occur in areas where very strong winds are mostly unidirectional. Although these dunes are found in areas now characterized by variable wind speeds,

360-407: A low-lying pan within the basin where the water evaporates, depositing the gypsum and forming crystals known as selenite . The crystals left behind by this process are eroded by the wind and deposited as vast white dune fields that resemble snow-covered landscapes. These types of dune are rare, and only form in closed arid basins that retain the highly soluble gypsum that would otherwise be washed into

432-412: A significant role in minimizing wave energy as it moves onshore. As a result, coastal dunes, especially those in the foredune area affected by a storm surge , will retreat or erode. To counteract the damage from tropical activity on coastal dunes, short term post-storm efforts can be made by individual agencies through fencing to help with sand accumulation. How much a dune erodes during any storm surge

504-606: A small, independent private elementary school serve the district. The Richmond/Senator Milton Marks Branch and the Anza Branch of the San Francisco Public Library serve the Richmond District. In 1930 voters approved a city charter amendment that would increase funding to the library system so a new library could be built. John Reid, Jr., the architect, designed and landscaped the $ 57,117.29 new library, which

576-406: A southward direction. First Avenue was renamed Arguello Boulevard and 49th Avenue was renamed La Playa Street. Today, the first numbered avenue is 2nd Avenue, starting one block west of Arguello Boulevard, and the last is 48th Avenue near Ocean Beach. The avenue numbers increase incrementally, with the exception that what would be 13th Avenue is called Funston Avenue named for Frederick Funston ,

648-462: A star dune superimposed on its crest is the most common complex dune. Simple dunes represent a wind regime that has not changed in intensity or direction since the formation of the dune, while compound and complex dunes suggest that the intensity and direction of the wind has changed. The sand mass of dunes can move either windward or leeward, depending on if the wind is making contact with the dune from below or above its apogee. If wind hits from above,

720-437: A suburb of Melbourne , Australia . In 1917, the district was legally named "Park-Presidio District", chosen to avoid confusion between the district and the city of Richmond right across the bay. In spite of the official change, San Franciscans continued to use the old name. The name Park-Presidio remained on the books until January 2009, when newly elected Supervisor Eric Mar introduced legislation that officially renamed

792-804: A unidirectional wind. In the sheltered troughs between highly developed seif dunes, barchans may be formed, because the wind is constrained to be unidirectional by the dunes. Seif dunes are common in the Sahara. They range up to 300 m (980 ft) in height and 300 km (190 mi) in length. In the southern third of the Arabian Peninsula, a vast erg , called the Rub' al Khali or Empty Quarter, contains seif dunes that stretch for almost 200 km (120 mi) and reach heights of over 300 m (980 ft). Linear loess hills known as pahas are superficially similar. These hills appear to have been formed during

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864-449: Is a landform composed of wind- or water-driven sand . It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex . A large dune complex is called a dune field , while broad, flat regions covered with wind-swept sand or dunes, with little or no vegetation, are called ergs or sand seas . Dunes occur in different shapes and sizes, but most kinds of dunes are longer on

936-477: Is a type of sandstone that is formed when a marine or aeolian sand dune becomes compacted and hardened. Once in this form, water passing through the rock can carry and deposit minerals, which can alter the colour of the rock. Cross-bedded layers of stacks of lithified dunes can produce the cross-hatching patterns, such as those seen in Zion National Park in the western United States. A slang term, used in

1008-442: Is a very large aeolian landform, with a length of several kilometers and a height of tens to hundreds of meters, and which may have superimposed dunes. Dunes are made of sand-sized particles, and may consist of quartz, calcium carbonate, snow, gypsum, or other materials. The upwind/upstream/upcurrent side of the dune is called the stoss side; the downflow side is called the lee side. Sand is pushed (creep) or bounces ( saltation ) up

1080-479: Is between Inner Richmond (to the east) and Outer Richmond (to the west). It is bounded by Park Presidio Blvd to the east, California St. to the north, Fulton St. to the south, and 32nd Ave. to the west. Its hub is on Geary Blvd. (between Park Presidio Blvd. to 28th Avenue). Within Central Richmond, in the area around Geary between about 17th Ave and 27th Ave, is sometimes called Little Russia. Outer Richmond

1152-410: Is blown along the beach. Dunes form where the beach is wide enough to allow for the accumulation of wind-blown sand, and where prevailing onshore winds tend to blow sand inland. The three key ingredients for coastal dune formation are a large sand supply, winds to move said sand supply, and a place for the sand supply to accumulate. Obstacles—for example, vegetation, pebbles and so on—tend to slow down

1224-688: Is bordered by Golden Gate Park on the south, the Pacific Ocean to the west, and Lincoln Park , Mountain Lake Park and the Presidio of San Francisco to the north, bisected by the Presidio Greenbelt. The neighborhood was given its name by Australian immigrant and art dealer George Turner Marsh, one of the neighborhood's earliest residents, who called his home "the Richmond House" after Richmond ,

1296-445: Is by saltation , where sand particles skip along the ground like a bouncing ball . When these skipping particles land, they may knock into other particles and cause them to move as well, in a process known as creep . With slightly stronger winds, particles collide in mid-air, causing sheet flows . In a major dust storm , dunes may move tens of metres through such sheet flows. Also as in the case of snow, sand avalanches , falling down

1368-428: Is due to a number of pressures related to their proximity to the ocean and confinement to growth on sandy substrates. These include: Plants have evolved many adaptations to cope with these pressures: In deserts where large amounts of limestone mountains surround a closed basin , such as at White Sands National Park in south-central New Mexico , occasional storm runoff transports dissolved limestone and gypsum into

1440-404: Is related to its location on the coastal shoreline and the profile of the beach during a particular season. In those areas with harsher winter weather, during the summer a beach tends to take on more of a convex appearance due to gentler waves, while the same beach in the winter may take on more of a concave appearance. As a result, coastal dunes can get eroded much more quickly in the winter than in

1512-660: Is to the west of the Central Richmond. It is bounded by Clement St. to the north, 32nd Ave. to the east, Fulton St. to the south, and Ocean Beach to the west. It borders the Ocean Beach and the Cliff House , currently operating as a restaurant. Lincoln Manor is a small enclave of larger homes within the Outer Richmond. It includes a vibrant merchant corridor on the western portion of Balboa St. from approximately 32nd Ave. to 42nd Ave. called Balboa Village . The Richmond District and

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1584-512: The Western Desert of Egypt . The largest crescentic dunes on Earth, with mean crest-to-crest widths of more than three kilometres, are in China's Taklamakan Desert . Abundant barchan dunes may merge into barchanoid ridges, which then grade into linear (or slightly sinuous) transverse dunes, so called because they lie transverse, or across, the wind direction, with the wind blowing perpendicular to

1656-454: The southwest US , for consolidated and hardened sand dunes is "slickrock", a name that was introduced by pioneers of the Old West because their steel-rimmed wagon wheels could not gain traction on the rock. Sand dunes can have a negative impact on humans when they encroach on human habitats. Sand dunes move via a few different means, all of them helped along by wind. One way that dunes can move

1728-659: The stoss (upflow) side, where the sand is pushed up the dune, and have a shorter slip face in the lee side. The valley or trough between dunes is called a dune slack . Dunes are most common in desert environments, where the lack of moisture hinders the growth of vegetation that would otherwise interfere with the development of dunes. However, sand deposits are not restricted to deserts, and dunes are also found along sea shores, along streams in semiarid climates, in areas of glacial outwash , and in other areas where poorly cemented sandstone bedrock disintegrates to produce an ample supply of loose sand. Subaqueous dunes can form from

1800-516: The 1950s, and especially after the lifting of the Chinese Exclusion Act in 1965, Chinese immigrants began to replace the ethnic Jewish and Irish-Americans who had dominated the district before World War II . Chinese of birth or descent now make up nearly the half of residents in the Richmond. Located directly north of Golden Gate Park , "the Richmond" is bounded roughly by Fulton Street to

1872-454: The 2 bus runs on Clement, and 1 bus runs on California. The Richmond has been popularly divided into four parts: Lake Street is just south of Presidio of San Francisco and north of Inner Richmond. It is an affluent area characterized by its many Victorian/Edwardian mansions. Its boundaries are: the Presidio to the north, Arguello Blvd to the east, California St. to the south, and 25th Ave. to

1944-686: The Outside Lands were a Mexican possession until the Treaty of Guadalupe Hidalgo in February 1848 ceded it to the United States . The area was U.S. government land at the time of the Gold Rush . The City and County of San Francisco, which was growing rapidly, desired the land and petitioned for it in the 1850s. After years of court battles, on March 8, 1866, Congress passed an Act ending the litigation and settling

2016-473: The Outside Lands, at a cost of $ 12,000. Their report recommending subdivision into blocks and a reservation for a park was submitted to the Board on May 18, 1866. Suitable portions were also to be set aside for public squares, fire-engine house lots, school lots and hospitals. The committee also proposed an arrangement whereby squatters could donate a portion of their claims for a public park in return for clear title to

2088-600: The Park. North of the Park in the Richmond District, the streets are named Anza , Balboa , and Cabrillo . Major parks in the Richmond District include: The Richmond is home to San Francisco Unified School District elementary, middle and high schools. Elementary schools have distinct attendance zones. George Washington High School is located in Outer Richmond, at 32nd Avenue and Anza St. Additionally, Katherine Delmar Burke School , an independent girls' school for kindergarten through eighth grade, as well as Kittredge School,

2160-513: The Richmond and to downtown . Technically, the Farallon Islands , about 30 miles to the west of mainland San Francisco, are also part of the Richmond District. The Richmond is easy to access by the 38R (Rapid) or 38 bus, which is around a 35 minutes bus ride from downtown running on a red bus lane. It is around a 15 minutes walk to GG Park taking the 38 bus. The 5 bus goes on Fulton to get to Golden Gate Park directly. The 31 bus runs on Balboa,

2232-551: The action of water flow ( fluvial processes) on sand or gravel beds of rivers , estuaries , and the sea-bed. Some coastal areas have one or more sets of dunes running parallel to the shoreline directly inland from the beach . In most cases, the dunes are important in protecting the land against potential ravages by storm waves from the sea . Artificial dunes are sometimes constructed to protect coastal areas. The dynamic action of wind and water can sometimes cause dunes to drift, which can have serious consequences. For example,

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2304-529: The area north of Golden Gate Park and west of Arguello Boulevard the Richmond District. The Richmond District, originally an expanse of rolling sand dunes called Outside Lands , was developed initially in the late 19th century. Before this development, the Yelamu Tribe of the Ohlone Nation frequented the coastal sites of the current day district and had a village where the development would take place. In

2376-409: The coastal environment of the sand dune vital to their species' survival. Over the course of time coastal dunes may be impacted by tropical cyclones or other intense storm activity, dependent on their location. Recent work has suggested that coastal dunes tend to evolve toward a high or low morphology depending on the growth rate of dunes relative to storm frequency. During a storm event, dunes play

2448-604: The concave sides of the dunes. These dunes form under winds that blow consistently from one direction (unimodal winds). They form separate crescents when the sand supply is comparatively small. When the sand supply is greater, they may merge into barchanoid ridges, and then transverse dunes (see below). Some types of crescentic dunes move more quickly over desert surfaces than any other type of dune. A group of dunes moved more than 100 metres per year between 1954 and 1959 in China 's Ningxia Province , and similar speeds have been recorded in

2520-651: The contract to survey park land, completed his report on February 15, 1871, and in August of the same year, was appointed as engineer of the park. Initial work completed in 1871 included grading, fencing, drainage and irrigation work, and development of a park nursery. In 1872, 22,000 hardy and quick-growing trees were planted, park roads were built, and visitors began to arrive by the thousands. 37°46′7.25″N 122°28′53.74″W  /  37.7686806°N 122.4815944°W  / 37.7686806; -122.4815944 Richmond District, San Francisco, California The Richmond

2592-405: The corridors between individual dunes. Because all dune arms are oriented in the same direction, and, the inter-dune corridors are generally swept clear of loose sand, the corridors can usually be traversed in between the trailing arms of the dune. However to cross straight over the dune by going over the trailing arms, can be very difficult. Also, traversing the nose is very difficult as well because

2664-491: The direction (s) of prevailing winds, are known as lunettes, source-bordering dunes, bourrelets and clay dunes. They may be composed of clay, silt, sand, or gypsum, eroded from the basin floor or shore, transported up the concave side of the dune, and deposited on the convex side. Examples in Australia are up to 6.5 km long, 1 km wide, and up to 50 metres high. They also occur in southern and West Africa , and in parts of

2736-657: The distance between the water line and where vegetation can grow. Coastal dunes can be classified by where they develop, or begin to take shape. Dunes are commonly grouped into either the Primary Dune Group or the Secondary Dune Group. Primary dunes gain most of their sand from the beach itself, while secondary dunes gain their sand from the primary dune. Along the Florida Panhandle, most dunes are considered to be foredunes or hummocks. Different locations around

2808-604: The dune and underlying soils . The stability of the dunes was once attributed to the vegetative cover but recent research has pointed to water as the main source of parabolic dune stability. The vegetation that covers them—grasses, shrubs, and trees—help anchor the trailing arms. In inland deserts, parabolic dunes commonly originate and extend downwind from blowouts in sand sheets only partly anchored by vegetation. They can also originate from beach sands and extend inland into vegetated areas in coastal zones and on shores of large lakes. Most parabolic dunes do not reach heights higher than

2880-513: The dunes and provide horticultural benefits, but instead spread taking land away from native species. Ammophila arenaria , known as European beachgrass, has a similar story, though it has no horticulture benefits. It has great ground coverage and, as intended, stabilized the dunes but as an unintended side effect prevented native species from thriving in those dunes. One such example is the dune field at Point Reyes, California . There are now efforts to get rid of both of these invasive species. As

2952-593: The dunes, washing humus into the slacks, and the slacks may be much more developed than the exposed tops of the dunes. It is usually in the slacks that more rare species are developed and there is a tendency for the dune slacks' soil to be waterlogged where only marsh plants can survive. In Europe these plants include: creeping willow, cotton grass, yellow iris , reeds, and rushes. As for vertebrates in European dunes, natterjack toads sometimes breed here. Dune ecosystems are extremely difficult places for plants to survive. This

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3024-592: The dunes. Typically these are heather , heaths and gorses . These too are adapted to the low soil water content and have small, prickly leaves which reduce transpiration. Heather adds humus to the soil and is usually replaced by coniferous trees, which can tolerate low soil pH , caused by the accumulation and decomposition of organic matter with nitrate leaching. Coniferous forests and heathland are common climax communities for sand dune systems. Young dunes are called yellow dunes and dunes which have high humus content are called grey dunes . Leaching occurs on

3096-401: The effective winds associated with the growth and migration of both the parabolic and crescent dunes probably are the most consistent in wind direction. The grain size for these well-sorted, very fine to medium sands is about 0.06 to 0.5 mm. Parabolic dunes have loose sand and steep slopes only on their outer flanks. The inner slopes are mostly well packed and anchored by vegetation, as are

3168-519: The geological record . All these dune shapes may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). Simple dunes are basic forms with the minimum number of slipfaces that define the geometric type. Compound dunes are large dunes on which smaller dunes of similar type and slipface orientation are superimposed. Complex dunes are combinations of two or more dune types. A crescentic dune with

3240-595: The globe have dune formations unique to their given coastal profile. Coastal sand dunes can provide privacy and/or habitats to support local flora and fauna. Animals such as sand snakes, lizards, and rodents can live in coastal sand dunes, along with insects of all types. Often the vegetation of sand dunes is discussed without acknowledging the importance that coastal dunes have for animals. Further, some animals, such as foxes and feral pigs can use coastal dunes as hunting grounds to find food. Birds are also known to utilize coastal dunes as nesting grounds. All these species find

3312-408: The harsh conditions of the foredune, typically having deep roots which reach the water table , root nodules that produce nitrogen compounds, and protected stoma , reducing transpiration . Also, the deep roots bind the sand together, and the dune grows into a foredune as more sand is blown over the grasses. The grasses add nitrogen to the soil, meaning other, less hardy plants can then colonize

3384-478: The last ice age under permafrost conditions dominated by sparse tundra vegetation. Star dunes are pyramidal sand mounds with slipfaces on three or more arms that radiate from the high center of the mound. They tend to accumulate in areas with multidirectional wind regimes. Star dunes grow upward rather than laterally. They dominate the Grand Erg Oriental of the Sahara. In other deserts, they occur around

3456-550: The later 18th century, they were not able to use this land anymore after Spanish explorers arrived and began setting up missions with the intent of converting and displacing the Ohlone people. Adolph Sutro was one of the first large-scale developers of the area. After purchasing the Cliff House in the early 1880s, he built the Sutro Baths on the western end, near Ocean Beach . After the 1906 earthquake , development increased with

3528-515: The margins of the sand seas , particularly near topographic barriers. In the southeast Badain Jaran Desert of China, the star dunes are up to 500 metres tall and may be the tallest dunes on Earth. Oval or circular mounds that generally lack a slipface. Dome dunes are rare and occur at the far upwind margins of sand seas. Fixed crescentic dunes that form on the leeward margins of playas and river valleys in arid and semiarid regions in response to

3600-502: The need to provide replacement housing. The last of the sand dunes and coastal scrub that once dominated the area were built over to create a streetcar suburb . The Russian Revolution and subsequent civil war brought many Anti-Communist White Russian , Orthodox Russian refugees and immigrants into the neighborhood. Russian Orthodox Church Outside Russia briefly made its headquarters at Holy Virgin Cathedral on Geary Boulevard. In

3672-546: The neighboring Sunset District (on the south side of Golden Gate Park) are often collectively known as "The Avenues", because a majority of both neighborhoods are spanned by numbered north–south avenues. When the city was originally laid out, the avenues were numbered from 1st to 49th and the east–west streets were lettered A to X. In 1909, to reduce confusion for mail carriers, the east–west streets and 1st Avenue and 49th Avenue were renamed. The east–west streets were named after Spanish explorers in ascending alphabetical order in

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3744-654: The nose is usually made up of loose sand without much if any vegetation. A type of extensive parabolic dune that lacks discernible slipfaces and has mostly coarse grained sand is known as a zibar . The term zibar comes from the Arabic word to describe "rolling transverse ridges ... with a hard surface". The dunes are small, have low relief, and can be found in many places across the planet from Wyoming (United States) to Saudi Arabia to Australia. Spacing between zibars ranges from 50 to 400 metres and they do not become more than 10 metres high. The dunes form at about ninety degrees to

3816-520: The point where he stayed. Inner Richmond sits south of Lake Street. Its boundaries are: California St. to the north, Arguello Blvd to the east, Fulton St. to the south, and Park Presidio Blvd. to the west. The hub of the Inner Richmond is Geary Blvd & Clement St, which are particularly known for Chinese, Thai, Korean, Burmese, and Russian cuisine. The Inner Richmond is a diverse area with sizable Chinese and Russian populations. Central Richmond

3888-440: The prevailing wind which blows away the small, fine-grained sand leaving behind the coarser grained sand to form the crest. Occurring wherever winds periodically reverse direction, reversing dunes are varieties of any of the above shapes. These dunes typically have major and minor slipfaces oriented in opposite directions. The minor slipfaces are usually temporary, as they appear after a reverse wind and are generally destroyed when

3960-600: The remainder of their lands. The proposal won Supervisor McCoppin the Mayor’s office, and gained the approval of the state legislature. On April 4, 1870, the state legislature passed “An Act to provide for the improvement of Public Parks in the City of San Francisco” Soon after, the newly formed park commission advertised bonds to fund park improvements. Enough bonds were sold to finance a topographical survey of Golden Gate Park and its approach. Surveyor and engineer William Hammond Hall won

4032-478: The resultant direction of sand movement (hence the name "longitudinal"). Some linear dunes merge to form Y-shaped compound dunes. Formation is debated. Ralph Bagnold , in The Physics of Blown Sand and Desert Dunes , suggested that some seif dunes form when a barchan dune moves into a bidirectional wind regime, and one arm or wing of the crescent elongates. Others suggest that seif dunes are formed by vortices in

4104-475: The ridge crest. Seif dunes are linear (or slightly sinuous) dunes with two slip faces. The two slip faces make them sharp-crested. They are called seif dunes after the Arabic word for "sword". They may be more than 160 kilometres (100 miles) long, and thus easily visible in satellite images (see illustrations). Seif dunes are associated with bidirectional winds. The long axes and ridges of these dunes extend along

4176-415: The sand in the dune migrates forward. In plan view, these are U-shaped or V-shaped mounds of well-sorted, very fine to medium sand with elongated arms that extend upwind behind the central part of the dune. There are slipfaces that often occur on the outer side of the nose and on the outer slopes of the arms. These dunes often occur in semiarid areas where the precipitation is retained in the lower parts of

4248-425: The sand particles move leeward; the leeward flux of sand is greater than the windward flux. Conversely, if sand hits from below, sand particles move windward. Further, if the wind is carrying sand particles when it hits the dune, the dune's sand particles will saltate more than if the wind had hit the dune without carrying sand particles. Coastal dunes form when wet sand is deposited along the coast and dries out and

4320-438: The sea. A nabkha , or coppice dune, is a small dune anchored by vegetation. They usually indicate desertification or soil erosion, and serve as nesting and burrow sites for animals. Sub-aqueous ( underwater ) dunes form on a bed of sand or gravel under the actions of water flow. They are ubiquitous in natural channels such as rivers and estuaries, and also form in engineered canals and pipelines. Dunes move downstream as

4392-401: The south, Arguello Boulevard and Laurel Heights to the east, The Presidio , Lincoln Park , and Sea Cliff to the north, and Ocean Beach to the west. The western portion, "Outer Richmond", and the eastern portion, "Inner Richmond", are divided by a major thoroughfare, Park Presidio Boulevard ( California State Route 1 ). Geary Boulevard is a major east–west thoroughfare that runs through

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4464-402: The steeper slip face facing downstream. Ripple marks preserved in sedimentary strata in the geological record can be used to determine the direction of current flow, and thus an indication of the source of the sediments. Dunes on the bed of a channel significantly increase flow resistance, their presence and growth playing a major part in river flooding . A lithified (consolidated) sand dune

4536-604: The stoss side, and slides down the lee side. A side of a dune that the sand has slid down is called a slip face (or slipface). The Bagnold formula gives the speed at which particles can be transported. Five basic dune types are recognized: crescentic, linear, star, dome, and parabolic. Dune areas may occur in three forms: simple (isolated dunes of basic type), compound (larger dunes on which smaller dunes of same type form), and complex (combinations of different types). Barchan dunes are crescent-shaped mounds which are generally wider than they are long. The lee-side slipfaces are on

4608-663: The summer. The converse is true in areas with harsher summer weather. There are many threats to these coastal communities. Some coastal dunes, for example ones in San Francisco, have been completely altered by urbanization; reshaping the dune for human use. This puts native species at risk. Another danger, in California and places in the UK specifically, is the introduction of invasive species. Plant species, such as Carpobrotus edulis , were introduced from South Africa in an attempt to stabilize

4680-421: The title to the Outside Lands against the claims of squatters. During the course of lengthy litigation over the Outside Lands, local politicians, led by Frank McCoppin , and residents of San Francisco, rallied for the establishment of a public park in the western quarter of the city. Mayor Henry P. Coon worked with a three-member special committee of the Board of Supervisors, which had surveys and maps made of all

4752-509: The town of Eucla, Western Australia , had to be relocated in the 1890s because of dune drift. The modern word "dune" came into English from French around 1790, which in turn came from Middle Dutch dūne . A universally precise distinction does not exist between ripples, dunes, and draas , which are all deposits of the same type of materials. Dunes are generally defined as greater than 7 cm tall and may have ripples, while ripples are deposits that are less than 3 cm tall. A draa

4824-471: The upstream slope is eroded and the sediment deposited on the downstream or lee slope in typical bedform construction. In the case of sub-aqueous barchan dunes, sediment is lost by their extremities, known as horns. These dunes most often form as a continuous 'train' of dunes, showing remarkable similarity in wavelength and height. The shape of a dune gives information about its formation environment. For instance, rivers produce asymmetrical ripples, with

4896-579: The west. Its name is derived from its proximity to Mountain Lake, one of the few remaining natural lakes in San Francisco, and Lake Street, the neighborhood's northernmost east–west artery. Spanish explorer Juan Bautista de Anza ended his second northward expedition at the lake, stopping for two days in 1776. While here he located a site for the Spanish presidio that was later built. A plaque was placed in September 1957 near

4968-534: The western United States, especially Texas. U-shaped mounds of sand with convex noses trailed by elongated arms are parabolic dunes. These dunes are formed from blowout dunes where the erosion of vegetated sand leads to a U-shaped depression. The elongated arms are held in place by vegetation; the largest arm known on Earth reaches 12 km. Sometimes these dunes are called U-shaped, blowout , or hairpin dunes, and they are well known in coastal deserts. Unlike crescent shaped dunes, their crests point upwind. The bulk of

5040-402: The wind and lead to the deposition of sand grains. These small "incipient dunes or "shadow dunes" tend to grow in the vertical direction if the obstacle slowing the wind can also grow vertically (i.e., vegetation). Coastal dunes expand laterally as a result of lateral growth of coastal plants via seed or rhizome . Models of coastal dunes suggest that their final equilibrium height is related to

5112-483: The wind next blows in the dominant direction. Draas are very large-scale dune bedforms; they may be tens or a few hundreds of metres in height, kilometres wide, and hundreds of kilometres in length. After a draa has reached a certain size, it generally develops superimposed dune forms. They are thought to be more ancient and slower-moving than smaller dunes, and to form by vertical growth of existing dunes. Draas are widespread in sand seas and are well-represented in

5184-568: Was placed on the site of the former Lafayette School. On April 10, 1932, the Anza Library, the 17th municipal library branch, was dedicated. In May 2009 the library system closed the Anza Branch for repairs. A rebuilt library opened on June 18, 2011. Jing Mo Athletic Association lion dancers provided entertainment at the ceremony. [REDACTED] Media related to Richmond District, San Francisco at Wikimedia Commons Sand dune A dune

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