Date of this Version
Published in Geological Survey Water-Supply Paper 1368 (1956) 76 pages.
The upper Niobrara River drainage basin comprises about 6,600 square miles in northwestern Nebraska and east-central Wyoming. The western half consists chiefly of rolling plains broken on either side of the Niobrara River by canyons of intermittent tributary streams; the eastern half is in the Sand Hills region of Nebraska.
Rocks ranging in age from Precambrian to Quaternary are exposed in the area described in this report. The pre-Tertiary rocks crop out only in a small area near Lusk, Wyo., and are not important as a source of water. Most of the area is underlain at considerable depth by the Chadron and Brule formations of Tertiary age, but they are not known to crop out. These rocks are not penetrated by wells because large quantities of water are available from shallower formations.
The Arikaree group and Ogallala formation, both' of Tertiary age, consist of fine-grained sand and sandstone, silt, and locally of many layers of limy concretions. These units are the principal aquifers, but they are only moderately permeable; consequently, most wells must penetrate 150 to 200 feet into the zone of saturation to obtain a large yield.
Dune sand, alluvium, and terrace deposits of Quaternary age are probably the most permeable sediments, but the zone of saturation in these deposits is not sufficiently thick to yield large quantities of water; therefore, large-discharge wells must be drilled into the underlying Tertiary rocks.