News Release, Kansas Geological Survey, Jan. 22, 1995
The full-color map was compiled by Allen Archer and Brian Smith of the Kansas State University geology department.
The map shows the age and type of rocks and soils at the surface of Riley County, ranging from relatively recent soils atop hills and sands and gravels along rivers, to bedrock in southeastern Riley County that was deposited during the Pennsylvanian Period of geologic history, approximately 300 million years ago.
Much of the county's bedrock is limestone and shale of Permian age, deposited about 250 million years ago at the bottom of a shallow sea. Some of those Permian limestones contain chert, or flint, the rock that gave the Flint Hills their name.
Because geologic maps provide basic information about an area's geology, they are useful in construction, city and county planning, and in a variety of environmental activities.
"Riley County displays many different types of bedrock, more than most areas of Kansas," said Archer. "This makes the map particularly important in construction and engineering projects, especially as development continues in the county."
In addition, the map shows the location of a dozen kimberlites, or pipes of igneous rock that exploded to the surface in western Riley County during the Cretaceous Period, approximately 100 million years ago.
"Flooding in 1993 exposed rock formations in the Tuttle Creek spillway, greatly increasing the interest in geology in Riley County," said Archer. "This map provides additional information on the geology of all of Riley County."
The Riley County map, one in a series of new geologic maps of Kansas counties being produced by the Survey, was drawn at a scale of 1:50,000, so that one inch on the map equals about 0.8 of a mile of actual distance. The map measures 48 by 40 inches. In addition to geology, the map shows roads, streams, towns, and lakes.