Geologic units in Phillips county, Colorado

Ogallala Fm (Tertiary) at surface, covers 82 % of this area

Loose to well-cemented sand and gravel

Eolian deposits (Quaternary) at surface, covers 18 % of this area

Includes dune sand and silt and Peoria Loess

Ogallala Group or Formation (Miocene) at surface, covers 0.3 % of this area

Silt, sand, sandstone, gravel and conglomerate. Predominantly interfingered fine- to coarse grained, poorly sorted, arkosic, fluvial deposits of light-gray, light-olive-gray, and grayish-green calcareous silt and sand, and locally poorly consolidated conglomerate, sandstone, and siltstone.