Rocks and minerals of the Chautauqua Hills

Sandstone. The characteristic rocks in the Chautauqua Hills are the thick sandstones that cap the hills and are exposed along creek and river valleys. Sandstone, which is made up largely of quartz grains cemented together by calcium carbonate, iron oxide, or silica, is a common sedimentary rock. In eastern Kansas, sandstone is often interbedded with shale and limestone. It also occurs as channel deposits, cutting through older deposits of shale and limestone.

The sandstones capping the Chautauqua Hills are the Tonganoxie Sandstone Member of the Stranger Formation and Ireland Sandstone Member of the Lawrence Formation. Both are thick rock formations, the remains of deposits that filled a large, ancient river valley during the Pennsylvanian subperiod.

Some sandstones are marked by ridges and troughs that look like the ripples you'd see in loose sand in a stream, shallow lake, sea, or sand dune. By studying ripple marks preserved in sandstone and comparing them with similar marks found in today's sand, geologists can make shrewd assumptions about what the environment was like when these sandstones were deposited. Fossil ripple marks provide information about the direction of the current, the environment, and, to a degree, the depth of the water. Some researchers believe that wind-created ripples are not preserved and that virtually all fossil ripple marks were formed in water.