Labels:text | screenshot | number | font | menu OCR: Geologic Studies of the Platte River, South-Central Nebraska and Adjacent Areas The Platte River of south-central Nebraska was studied at three scales to place the river in its geological context and to trace its evolution through late Miocene to the Pliocene and included the capture and diversion of the South Platte River into its present channel. The combined North and geologic time. At the largest scale the Elm Creek West and the Newark 7.5 minute quadrangles were mapped. These quadrangles are located just South Platte Rivers deposited gravel and sand across Nebraska and flowed west and just east of Kearney and serve to illustrate the main geomorphic southeast from Kearney, Nebraska through the middle to late Pleistocene. Within the past 25,000 years the Platte River below Kearney was captured elements of the present Platte River Valley. The central elements of the quadrangles are the Platte River channels, islands, and bottomlands, which and diverted into its present course and confined there by bounding valley are flanked by terraces that step up away from the river to the north and walls of loess. south. Significant other elements of the landscape are eolian sand and loess deposits. The geologic maps are supplemented by topographic profiles of the mapped terraces and graphical representations of System Requirements subsurface units in test wells that occur within the quadrangles. Windows An intermediate-scale study consisted of examining descriptions of well Intel® Pentium® or Xeon® or equivalent, 800 MHz minimum, 1.0GHz or cuttings in a 17 county area in south-central Nebraska, which includes the higher recommended . Platte River Valley, and building a database of information about sediment Microsoft® Windows® 2000, or Windows XP . lithology and thickness. The wells penetrated a sequence of gravel, sand, 256 MB minimum of RAM, 512 MB or higher recommended silt, and clay beds from the ground surface to the top of the subsurface Macintosh . Tertiary Ogallala Group or Cretaceous formations. The sequence consists PowerPC® processor of Pliocene -, Pleistocene -, and Holocene-age strata that document the . Mac OS software version 9.0.4, 9.1, 9.2, or OS X deposition of a veneer of alluvium by late Tertiary and Quaternary streams . 128 MB of RAM intermixed with and overlain by wind-blown loess. Various isopleth and UNIX structure maps illustrate the distribution and alluvial architecture of the . Most UNIX system-based, and Linux platforms should be capable of sedimentary sequence, and support the interpretation of former positions of the Platte River. manipulating these files. A regional-scale study consisted of documenting the geologic history All platforms . of the Front Range and adjacent mountains and depositional areas east of VGA color monitor that can display 256 colors (16.7 million colors the mountains in Colorado, Wyoming, Kansas, and Nebraska from the end recommended) of the Cretaceous Period, about 65 million years ago, to the present. The . Adobe® Reader 6.0 or higher or other software that can translate Portable structural and sedimentary history of the region is outlined, and a series of Document Format (PDF) files paleogeographic maps shows the development of the drainage system in . Web browser such as Firefox, Camino, Safari, Microsoft Internet Explorer, the east-central Rocky Mountains and adjacent Plains. Ancestral South Netscape Browser version 7.0 or greater Platte, North Platte, and Laramie Rivers are recognized as early as the . GIS software capable of reading ESRI® shapefile format is needed to take late Eocene, although the South Platte probably flowed to the southeast full advantage of the GIS-capabilities of this publication from the mountain front at that time. Deposits of the North Platte River are recognized on the west side of the Medicine Bow Mountains of Wyoming Any use of trade, product, or firm names is for descriptive purposes only and in the Miocene, and the presence of distinctive rock clasts indicates that does not imply endorsement by the U.S. Government. the Laramie River flowed from the North Park area of Colorado northeast across a filled Laramie Basin and the Laramie Range of southeastern This report and any updates to it are available online at Wyoming in the Miocene. The present drainage system developed in the http://pubs.usgs.gov/pp/pp1706/ ISBN 0-411-30507-7 U.S. DEPARTMENT OF THE INTERIOR Gale Norton, Secretary COMPACT DISC HFS Q66o U.S. GEOLOGICAL SURVEY P. Patrick Leahy, Acting Director DATA STORAGE 9 780411 305079
