Geologic units in Crowley county, Colorado

Eolian deposits (Quaternary) at surface, covers 33 % of this area

Includes dune sand and silt and Peoria Loess

Pierre Shale--Lower unit (Cretaceous) at surface, covers 22 % of this area

Sharon Springs Member (organic-rich shale and numerous bentonite beds) in lower part

Pierre Shale--Middle unit (Cretaceous) at surface, covers 21 % of this area

In Boulder-Fort Collins area, contains Richard, Larimer, Rocky Ridge, Terry, and Hygiene Sandstone Members; elsewhere shale between zones of Baculites reesidei and B. scotti

Older gravels and alluviums (Quaternary) at surface, covers 16 % of this area

Includes Slocum, Verdos, Rocky Flats, and Nussbaum Alluviums in east, and Florida, Bridgetimber, and Bayfield Gravels in southwest

Niobrara Fm (Cretaceous) at surface, covers 4 % of this area

Calcareous shale and limestone

Modern alluvium (Quaternary) at surface, covers 3 % of this area

Includes Piney Creek Alluvium and younger deposits

Gravels and alluviums (Quaternary) at surface, covers 0.9 % of this area

Includes Broadway and Louviers Alluviums

Pierre Shale--Upper unit (Cretaceous) at surface, covers 0.6 % of this area

Pierre Shale--Upper unit