Geologic units in Baca county, Colorado

Ogallala Fm (Tertiary) at surface, covers 61 % of this area

Loose to well-cemented sand and gravel

Eolian deposits (Quaternary) at surface, covers 23 % of this area

Includes dune sand and silt and Peoria Loess

Dakota Sandstone and Purgatoire Fm (Cretaceous) at surface, covers 9 % of this area

Sandstone and shale

Carlile Shale, Greenhorn Limestone, and Graneros Shale (Cretaceous) at surface, covers 5 % of this area

Carlile Shale, Greenhorn Limestone, and Graneros Shale

Morrison, Ralston Creek, and Entrada (or Exeter) Fms (Jurassic) at surface, covers 1 % of this area

Morrison, Ralston Creek, and Entrada (or Exeter) Fms

Dockum Group (Triassic) at surface, covers 0.4 % of this area

Red sandstone, siltstone, and local limestone

Modern alluvium (Quaternary) at surface, covers 0.4 % of this area

Includes Piney Creek Alluvium and younger deposits

Basalt flows and associated tuff, breccia, and conglomerate of late-volcanic bimodal suite (Tertiary) at surface, covers < 0.1 % of this area

Includes basalts of Hinsdale Fm in San Juan Mountains - Servilleta Fm in San Luis Valley and many other occurrences

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

Calcareous shale and limestone

Dakota Sandstone (Early Cretaceous) at surface, covers < 0.1 % of this area

CIMARRON- Buff to light-brown, fine- to medium-grained, thin bedded to massive sandstone with interbedded shales.

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.

Upper Permian rocks, undivided (Permian) at surface, covers < 0.1 % of this area

Siltstone, dolomite, and sandstone; in southeast

Upper and lower Cretaceous rocks of east-central and northeast New Mexico (Cenomanian and Albian) at surface, covers < 0.1 % of this area

Consists of Dakota Group, which includes Romeroville Sandstone (Cenomanian), Pajarito Shale, and Mesa Rica Sandstone (Albian); the underlying Tucumcari Shale (Albian) in Tucumcari area and Glencairn Formation (Albian) in Union County.

Morrison Formation and upper San Rafael Group (lowermost Cretaceous? - upper Jurassic) at surface, covers < 0.1 % of this area

Morrison Formation and upper San Rafael Group

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

CIMARRON- Varicolored fine-grained sandstone, limestone, dolomite, shale, and conglomerate 0 to 470 +/- feet thick.

Purgatoire Formation (Early Cretaceous) at surface, covers < 0.1 % of this area

CIMARRON- Kiowa Shale Member: Gray to black fossiliferous shale with sandstone in the upper part. Thickness ranges from 0 to 50 +/- feet. Cheyenne Sandstone Member: Massive, white to buff, fine- to medium-grained sandstone, containing some conglomerate in the lower part, from 0 to 120 +/- feet thick.

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

CIMARRON- Clay, silt, sand, and gravel 0 to 100 feet thick. TEXAS- Sand, silt, clay, and gravel located in valleys of principal streams. Thickness not known but may exceed 100 feet in North Canadian River valley and may be 50 to 100 feet in lower parts of valleys of Coldwater and Palo Duro Creeks BEAVER - Sand, gravel, silt, and clay in discontinuous lenses along courses of larger streams. 0-50 feet thick.

Dockum Group (Late Triassic) at surface, covers < 0.1 % of this area

CIMARRON- Upper shale unit: Varicolored siltstone or claystone, conglomerate, fine-grained sandstone, and limestone. Lower sandstone unit: Varicolored, fine- to coarse-grained sandstone with some clay and interbedded shale.

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.

Entrada Sandstone (Middle Jurassic) at surface, covers < 0.1 % of this area

Entrada Sandstone

Chinle Group (Upper to middle Triassic) at surface, covers < 0.1 % of this area

Map unit includes Moenkopi Formation (Middle Triassic) at base in many areas; in eastern part of state the following five formations are mapped: TRr, TRb, TRt, TRg, and TRs.

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

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

unconsolidated dune sand