Geology and ground-water resources of Platte County, Wyoming, with a section on Chemical quality of the water

Abstract

Platte County, Wyo., has an area of 2,114 square miles and, in 1950, had a population of 7,925; it lies within parts of two major physiographic provinces, the northern extension of the Southern Rocky Mountains and the northwestern part of the Great Plains. The Laramie Range and related structures lie along the western margin of the county and constitute the eastern limit of the Rocky Mountain Front Range. The High Plains section of the Great Plains province extends eastward from the Laramie Range over the remainder of the county. The original surface of the High Plains has been deeply eroded, and in the northeastern part of the county it is broken by the broad uplifted structural platform of the Hartville Hills. The North Platte River and its tributaries have entrenched their channels as much as 1,000 feet into the plains, leaving wide, very flat intervalley areas that are interrupted by a few isolated buttes and outlying ridges. Well-defined terraces, locally called the Wheatland Flats, have been formed in central Platte County. The climate is semiarid, the average annual precipitation being about 15 inches. Farming and stockraising are the principal occupations in the county. Most of the rocks exposed in the county are of Tertiary and Quaternary age, although rocks as old as Precambrian crop out locally. The Arikaree and Brule formations and younger deposits, including Tertiary ( ?) deposits (undifferentiated) and terrace, flood-plain, and other alluvial deposits, underlie more than two-thirds of the county. Mesozoic, Paleozoic, and Precambrian rocks crop out in the other third and underlie the younger rocks at great depths elsewhere. Small supplies of ground water adequate for domestic and stock use can be obtained from shallow wells in the Casper, Hartville, Cloverly, Brule, and Arikaree formations and in the terrace and flood-plain deposits. Small to moderate amounts of ground water can be obtained from the 'Converse sand' of the Hartville formation. Several flowing wells obtain water from this sand near Glendo. Moderate to large supplies of ground water adequate for small-scale irrigation or industrial uses or for public supply can be obtained from properly constructed wells penetrating thick saturated sections of the Arikaree formation and from the terrace and flood-plain deposits. Large supplies of ground water can be obtained from the flood-plain deposits of the North Platte River near Guernsey, where wells commonly yield more than 1,000 gpm (gallons per minute). The aquifers with greatest potential for additional groundwater development in Platte County, in decreasing order of importance, are the flood-plain deposits along the North Platte River and its tributaries, the Arikaree formation and terrace deposits in parts of the Wheatland Flats, and the 'Converse sand' in the general vicinity of Glendo.