News Release, Kansas Geological Survey, July 6, 2010
LAWRENCE--The surface geology of Finney County in southwestern Kansas is featured on a new full-color map available from the Kansas Geological Survey, based at the University of Kansas.
Geologic maps show the type and age of rock layers found at the surface or immediately under the vegetation and soil. This revised map expands on one produced in 1993 by KU Geography Professor William Johnson and Alan Arbogast, former KU graduate student and now professor at Michigan State University.
Revisions by Johnson and Terri Woodburn, KU geography graduate student, include terrace systems along the Arkansas and Pawnee rivers that were previously identified as floodplain alluvium as well as playa lakes.
Playa lakes, transient wetlands fed only by precipitation and runoff, range in size from less than an acre to hundreds of acres and are scattered on the uplands throughout the county. When wet, the small, shallow basins also known as lagoons or buffalo wallows help recharge the underlying High Plains aquifer and provide refuge for local and migratory wildlife.
"Finney County has a spectacular number of playas, nearly 1,700 of them, some of which originated several thousand years ago," Johnson said.
Much of Garden City, the county seat, and Holcomb are located in terrace deposits along the Arkansas River. Terraces are remnants of previous floodplains located at a higher elevation than the current river channels and their floodplains, which have cut down through the older deposits. Terrace fill consists mainly of coarse gravel with some sand and silt.
The Arkansas River, which crosses the southern portion of the county, has been mostly dry for the last three decades due to decreases in ground-water levels in the High Plains aquifer, the major source of water in western Kansas.
Surface geology in Finney County includes formations deposited from about 70 million to less than 1,000 years ago. Loess, or wind-blown silt, deposited within the last 100,000 years covers much of the county's surface, especially north of the Arkansas River.
A large area of inactive sand dunes, sand sheets, and alluvial deposits are located south of the Arkansas River. Sand and gravel from the alluvial deposits are used for road surfacing and concrete construction.
"Sand dunes in the county are spectacular features that have been active off and on during the last 15,000 years or so," Johnson said. "Prehistoric dune activity was usually far more severe than during the 1930's Dust Bowl."
In northeastern Finney County, Fort Hays limestone and Blue Hill shale, the oldest rock found at the surface in the county, crop out along the Pawnee River.
Outcrops of the Ogallala Formation adjacent to the Arkansas and Pawnee rivers are locally known as mortar beds. The formation is made up of silt, sand, gravel, and clay transported in by streams from the Rocky Mountains about 5 million years ago and underlies much of the county. The water-bearing portion of the formation, or Ogallala aquifer, is part of the High Plains aquifer system.
In addition to rock units and relief, the map shows towns, roads (from federal highways to unimproved roadways), ponds and streams, sand and gravel pits, and elevation contours at 10-meter intervals.
Drawn in full-color to differentiate rock layers, the computer-generated geologic map features shaded relief to give the map its three-dimensional look and emphasizes the landscape's topography. The map is at a scale of 1:50,000 so that one inch on the map equals about 3/4 mile of actual distance.
Besides the map, the 64" x 50" sheet contains an illustrated rock column, which classifies rock units on the map, and a description of each unit.
Copies of the Finney County map are available from the Kansas Geological Survey at 1930 Constant Ave., Lawrence, KS 66047-3724 (phone 785-864-3965, email pubsales@kgs.ku.edu) and at 4150 W. Monroe St., Wichita, KS, 67209-2640 (phone 316-943-2343, email wwsl@kgs.ku.edu).
The cost is $15 plus shipping and handling. Inquire about shipping and handling charges and, for Kansas residents, sales tax. More information about the maps and other KGS products is available at the Survey's web site (www.kgs.ku.edu).