Geologic units in Dallam county, Texas

Blackwater Draw Formation (Pleistocene) at surface, covers 41 % of this area

Blackwater Draw Formation

Sand sheet deposits (Holocene) at surface, covers 40 % of this area

Sand sheet deposits

Ogallala Formation (Pliocene to Miocene) at surface, covers 17 % of this area

Ogallala Formation

Dune sand sheet deposits (Holocene) at surface, covers 1 % of this area

Dune sand sheet deposits

Alluvium (Holocene) at surface, covers 0.5 % of this area

Alluvium

Playa deposits (Pleistocene and Holocene) at surface, covers 0.2 % of this area

Playa deposits

Terrace deposits (Pleistocene and Holocene) at surface, covers 0.2 % of this area

Terrace deposits

Sand dune deposits (Holocene) at surface, covers 0.2 % of this area

Sand dune deposits

Ogallala Formation (Pliocene) at surface, covers < 0.1 % of this area

CIMARRON- Generally semiconsolidated clay, silt, sand, gravel, and caliche 0 to 400 feet thick. BEAVER- Interbedded sand, siltstone, clay, gravel lenses, and thin limestone. Caliche common near surface but occurrence is not limited to the surface. Caliche accounts for most of the white color in the Ogallala. Other colors generally light tan or buff but locally may be pastel shades of almost any color. The Laverne and Rexroad Formations of Pliocene age and the Meade Group and Odee (of local usage) and other formations of Pleistocene age occur locally and are included with the Ogallala Formation, 0-700 feet thick. WOODWARD- Gravel, sand, silt, clay, caliche, and limestone, locally cemented with calcium carbonate. Generally light-tan to gray to white. Thickness ranges up to 400 feet and probably averages 150 feet. CLINTON- Gray to light-brown, fine- to medium-grained sand with some, clay, silt, gravel, volcanic ash, and caliche beds; locally cemented by calcium carbonate. Thickness ranges from 0 to about 320 feet. The formation thins eastward.

Morrison Formation (Late Jurassic) at surface, covers < 0.1 % of this area

Morrison Formation

Dakota and Purgatoir Formations, undivided (Early Cretaceous) at surface, covers < 0.1 % of this area

Dakota and Purgatoir Formations, undivided

Dune Sand (Pleistocene) at surface, covers < 0.1 % of this area

CIMARRON- Fine- to medium-grained sand 0 to 40 feet thick. TEXAS- Fine to coarse windblown sand. Maximum thickness about 30 feet. BEAVER- Fine to coarse, round to sub-round, windblown sand consisting mostly of quartz grains. 0-50 feet thick.

Eolian deposits (Holocene to middle Pleistocene) at surface, covers < 0.1 % of this area

Eolian deposits.

Dakota Formation (Early and Late Cretaceous) at surface, covers < 0.1 % of this area

Dakota Formation