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A "quadrangle" is a topographic map produced by the United States Geological Survey (USGS) covering the United States. The maps are usually named after local physiographic features. The shorthand "quad" is also used, especially with the name of the map; for example, "the Ranger Creek, Texas quad". A quadrangle is defined by north and south ...
During the Quaternary period, Illinois was subject to multiple intervals of glaciation; over 90% of Illinois was formerly covered by glaciers, leaving a variety of glacial landscape features. The Mississippi River, fed by ice-sheet melt and water from glacial lakes, cut a deep valley as it flowed through the region.
Geologic time is the timescale used to calculate dates in the planet's geologic history from its origin (currently estimated to have been some 4,600 million years ago) to the present day. Radiometric dating measures the steady decay of radioactive elements in an object to determine its age. It is used to calculate dates for the older part of ...
Today's U.S. Topo quadrangle (1:24,000) maps are mass-produced, using automated and semiautomated processes, with cartographic content supplied from the National GIS Database. [33] In the two years from June 2009 to May 2011, the USGS produced nearly 40,000 maps, more than 80 maps per work day. [33]
Shaded relief map of the United States, showing 10 geological provinces. The richly textured landscape of the United States is a product of the dueling forces of plate tectonics, weathering and erosion. Over the 4.5 billion-year history of the Earth, tectonic upheavals and colliding plates have raised great mountain ranges while the forces of ...
The Illinoian Stage is the name used by Quaternary geologists in North America to designate the Penultimate Glacial Period c.191,000 to c.130,000 years ago, during the late Middle Pleistocene (Chibanian), when sediments comprising the Illinoian Glacial Lobe were deposited.
The Everton Formation is a geologic formation in northern Arkansas through Missouri, Illinois and Indiana that dates to the middle Ordovician Period. [3] It was named by Ulrich (1907) for exposures found around Everton, Arkansas. Fossils of Conodonts Paraprioniodus costatus and Leptochirognathus quadratus indicate Whiterockian age. [4]
The geologic time scale is a way of representing deep time based on events that have occurred throughout Earth's history, a time span of about 4.54 ± 0.05 Ga (4.54 billion years). [3] It chronologically organises strata, and subsequently time, by observing fundamental changes in stratigraphy that correspond to major geological or ...