Geologic units in Cheyenne county, Colorado

Eolian deposits (Quaternary) at surface, covers 63 % of this area

Includes dune sand and silt and Peoria Loess

Ogallala Fm (Tertiary) at surface, covers 18 % of this area

Loose to well-cemented sand and gravel

Pierre Shale--Middle unit (Cretaceous) at surface, covers 8 % 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 5 % of this area

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

Pierre Shale--Upper unit (Cretaceous) at surface, covers 3 % of this area

Pierre Shale--Upper unit

Pierre Shale--Lower unit (Cretaceous) at surface, covers 2 % of this area

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

Modern alluvium (Quaternary) at surface, covers 0.5 % of this area

Includes Piney Creek Alluvium and younger deposits

Niobrara Fm (Cretaceous) at surface, covers 0.1 % of this area

Calcareous shale and limestone

Loess (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

eolian silts

Alluvium (Holocene to Pleistocene) at surface, covers < 0.1 % of this area

unconsolidated sand, silt, clay, and gravel