Geology and Ground-Water Resources of Allen County, Kansas

Allen County lies within the Osage Plains section of the Central Lowlands physiographic province and includes an area of about 504 square miles. Rocks above the Precambrian basement have an average thickness of about 2,000 feet and are all sedimentary in origin. The consolidated deposits range in age from Cambrian through Pennsylvanian, and the unconsolidated deposits range in age from probable Tertiary through Quaternary. Only rocks of Pennsylvanian, Tertiary(?), and Quaternary age are exposed in the county. The exposed Pennsylvanian rocks have a regional dip to the northwest of about 12 to 15 feet per mile. The most important bedrock aquifers are the shallow Pennsylvanian limestones and sandstones that have been weathered along joints, fractures, and bedding planes. Potable ground water is usually not found in the county below the base of the Kansas City Group, and in many places the boundary between fresh and saline water is much higher in the stratigraphic section. Alluvial deposits having an average thickness of about 25 feet in the Neosho River valley should yield 10 to 100 gallons per minute of ground water to wells. Where saturated, Illinoisan terrace deposits should yield moderate amounts of water to wells. In much of the valley, semi-artesian or artesian conditions probably prevail owing to a confining silt which overlies the permeable gravels. Water from the Quaternary deposits is of good quality but is usually very hard. Water derived from shallow bedrock aquifers is generally higher in dissolved solids content and hardness than water from the Quaternary deposits.