Geology

The Rathbun Lake Project area geology generally consists of a series of thick shale alternated with thin layers of clay, coal, limestone and sandstone. These bedrock layers are all of Pennsylvanian age and are deeply buried by glacial drift and loess deposits. The loess deposits are Wisconsin age and are on a Yarmouth-Sangamon paleosol, formed in Kansan till. The base of the loess is 16,500 to 24,000 years old; loess summits are 14,000 years old, and hill slopes are younger. Stepped topographic levels between divides and drainage may have Wisconsin loess on a Wisconsin erosion surface or Late Sangamon paleosol on Kansan drift. The glacial deposits generally extend to a depth of 125 feet. The loess layer above these deposits ranges from one to 18 feet deep (Ruhe 1969; US Army Engineer District, Kansas City 1975). The extensive erosion that occurs in the project area has washed away much of the original loess cover.