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21-515: The Jeffers Petroglyphs site is an outcrop in southwestern Minnesota with pre-contact Native American petroglyphs . The petroglyphs are pecked into rock of the Red Rock Ridge, a 23-mile (37 km)-long Sioux quartzite outcrop that extends from Watonwan County, Minnesota to Brown County, Minnesota . The exposed surface is approximately 150 by 650 feet (50 by 200 m) and surrounded by virgin prairie. "The site lies in an area inhabited in

42-461: A Dakota elder, was quoted as saying, "To the contemporary Native Americans who reside in and around the state, [Jeffers Petroglyphs] is a very spiritual place. It is a place where Grandmother Earth speaks of the past, present and future." The Minnesota Historical Society purchased the site from W. R. Jeffers, Jr. in 1966 and it was added to the National Register of Historic Places in 1970. It

63-558: A clear sky chart, showed all of Rahill's forecast data, but for only one location. Danko writes "It shows at a glance when, in the next 48 hours, we might expect clear and dark skies for one specific observing site". Danko accepts requests from observatories and private individuals to create new CSCs for locations not currently covered. However, since CMC's GEM model only covers North America, CSCs are limited to North America. In 2020, Danko added Norwegian/European forecast (ECMWF) information to some charts. Research continues as to which forecast

84-787: A continuous line along the top edge with lines protruding down; outcrops have a continuous line around each area of bare rock. An outcrop example in California is the Vasquez Rocks , familiar from location shooting use in many films , composed of uplifted sandstone . Yana is another example of outcrops, located in Uttara Kannada district in Karnataka , India . Clear Sky Chart Clear Sky Charts (called clocks until February 29, 2008) are web graphics which deliver weather forecasts designed specifically for astronomers . They forecast

105-411: A new forecast of cloud cover. Rahill specially designed his cloud forecast to consider the formation of cirrus clouds . The cirrus cloud modeling distinguishes Rahill's model from other cloud forecast models, as sufficient cirrus clouds to make a night unusable for astronomers is still called "clear" by civil weather forecasts. In later years, Rahill added a forecast of astronomical transparency, which

126-539: A record of relative changes within geologic strata . Accurate description, mapping, and sampling for laboratory analysis of outcrops made possible all of the geologic sciences and the development of fundamental geologic laws such as the law of superposition , the principle of original horizontality , principle of lateral continuity , and the principle of faunal succession . On Ordnance Survey maps in Great Britain , cliffs are distinguished from outcrops: cliffs have

147-548: Is a measure of how much starlight traverses the Earth's atmosphere when otherwise free of clouds. Rahill also added a forecast of astronomical seeing which uses forecast data of turbulence and temperature gradients in the atmosphere to forecast its optical steadiness. In 2001, Attilla Danko, computer programmer and amateur astronomer , began to summarize Rahill's hundreds of forecast maps by displaying only one pixel, from each map, laid out in rows. The resulting meteogram , called

168-665: Is limited to Canada, the USA and parts of Mexico and the Caribbean. Locations are typically cities, professional and public observatories , colleges and science centers . However there are also clear sky charts for star parties and backyard observatories. In 2000, Allan Rahill, a meteorologist at the Canadian Meteorological Centre (CMC) and amateur astronomer, created a forecast processing step that took data from CMC's Global Element Multi-scale (GEM) forecast model and created

189-684: Is maintained by the Minnesota Historical Society and is open to the public between May and September. The site is bracketed by two important tracts of tallgrass prairie : Rock Ridge Prairie Scientific and Natural Area to the northwest and Red Rock Prairie, a preserve of The Nature Conservancy , to the east. Here federally threatened prairie bush clover is found, as well as big bluestem , Indian grass , gray-headed coneflower , Maximilian's sunflower , cordgrass and coreopsis . The upland sandpiper , regal fritillary and Poweshiek skipper can be found on these prairies. The visitor center

210-512: Is more reliable. On February 29, 2008 Danko changed the name of the CSCs to "clear sky charts" to avoid any possibility of legal action on the part of Skyclock company of Michigan who owns a USA registered trademark on the name "SKYCLOCK". Danko's attorney opined that he was not infringing Skyclock Company's trademark, but also advised that changing the name was the "least painful" and least "expensive" solution. However, there continue to be references to

231-402: Is open from May through September and features hands-on exhibits and a multimedia presentation about the site. Daily natural and cultural history programs are offered about such topics as archaeology , how Native Americans made and used the atlatl , a travois and cordage , and prairie wildlife and plants. The Starry Night, Prairie Night event is held annually in the park. During this time

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252-402: Is rapid and exceeds the weathering rate such as on steep hillsides, mountain ridges and tops, river banks, and tectonically active areas. In Finland , glacial erosion during the last glacial maximum (ca. 11000 BC), followed by scouring by sea waves, followed by isostatic uplift has produced many smooth coastal and littoral outcrops. Bedrock and superficial deposits may also be exposed at

273-520: Is rated green by the Clear Sky Chart . Outcrop Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial deposits are covered by soil and vegetation and cannot be seen or examined closely. However, in places where the overlying cover is removed through erosion or tectonic uplift , the rock may be exposed, or crop out . Such exposure will happen most frequently in areas where erosion

294-405: The cloud cover , transparency and astronomical seeing , parameters which are not forecast by civil or aviation forecasts. They forecast hourly data, but are limited to forecasting at most 48 hours into the future. Each individual chart provides data for only a 9 mile radius, and so are essentially point forecasts. There are clear sky chart forecasts for over 6100 locations, though the coverage area

315-423: The Earth's surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis and creating geologic maps . In situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding the geologic time scale of earth history. Some of

336-557: The Late Archaic Period. Other carvings, such as thunderbirds , dragonflies, turtles, and shamans , indicate symbols used by later tribes such as the Otoe tribe , Sioux , and Iowa tribe . These are believed to date between 900 CE and 1750 CE. There are over 4000 American Indian images preserved in the bedrock. The bedrock was flattened and smoothed over by glaciers 14000 years ago. Several archaeologists have hypothesized theories about

357-536: The early historic period by the Dakota Indians , and both the style and form of some of the carvings are identical with motifs that appear on Dakota hide paintings and their quill designs and beadwork . Others are foreign to this Plains Indian tradition and seem to be much earlier in origin." Several old wagon trail ruts traverse the site, one of which is believed to be the old stage coach route from New Ulm, Minnesota to Sioux Falls, South Dakota . The exact age of

378-461: The park manager allows amateur astronomers to use the park and facilities. Many amateur astronomers attend this event and several members bring their telescopes and allow, and often encourage, others to share their views of the night sky. This site is valued not only because of its historic nature but also because of its dark night skies. The site is much darker than most populated areas in Minnesota and

399-537: The petroglyphs is not known, but the earliest petroglyphs are estimated to be from 9000 to 7000 years ago (7000 to 5000 BCE). but some atlatl symbols at Jeffers are a close match with similar symbols at Indian Knoll in Kentucky , which have been dated to 3000 BCE during the Late Archaic Period . Another clue to the age comes from the projectile point carvings, which show a projectile point design used by hunters in

420-496: The purpose of the carvings. Some hypotheses include the practice of hunting magic, performance of sacred ceremonies, or recording historical events in the lives of warriors, shamans, and chiefs. The exact age and purpose of the carvings is only speculation, not established fact. Meanwhile, some Native Americans view the Jeffers site as sacred ground and a very spiritual place, not merely a site to be studied and speculated upon. Jerry Flute,

441-468: The types of information that cannot be obtained except from bedrock outcrops or by precise drilling and coring operations, are structural geology features orientations (e.g. bedding planes, fold axes, foliation ), depositional features orientations (e.g. paleo-current directions, grading, facies changes), paleomagnetic orientations. Outcrops are also very important for understanding fossil assemblages, and paleo-environment, and evolution as they provide

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