Geologic units in Lincoln county, Colorado

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

Includes dune sand and silt and Peoria Loess

Pierre Shale--Upper unit (Cretaceous) at surface, covers 24 % of this area

Pierre Shale--Upper unit

Ogallala Fm (Tertiary) at surface, covers 24 % of this area

Loose to well-cemented sand and gravel

Older gravels and alluviums (Quaternary) at surface, covers 10 % of this area

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

Pierre Shale--Middle unit (Cretaceous) at surface, covers 6 % 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

Modern alluvium (Quaternary) at surface, covers 2 % of this area

Includes Piney Creek Alluvium and younger deposits

Pierre Shale--Lower unit (Cretaceous) at surface, covers 1.0 % of this area

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