Texas lignite occurs in three Eocene (lower Tertiary) geologic units--the Wilcox Group, Jackson Group, and Yegua Formation--and in three ancient depositional systems--fluvial, deltaic, and strandplain/lagoonal. Near-surface resources in Texas at depths between 20 and 200 ft (6.1 and 61 m) in seams 3 ft (0.9 m) or thicker are 23,377 million short tons (21,208 million metric tons) and are dominantly fluvial in origin. More than 90 percent of the resources occur in the Wilcox and Jackson Groups north of the Colorado River.

The Red Cave Formation (Permian, Leonard Series) in the Texas Panhandle consists of cyclic, red-bed clastic and carbonate-evaporite members that reflect deposition in extensive coastal sabkhas. These environments were bounded on the north by a desert wadi plain and on the south by a carbonate inner shelf that bordered the northern Midland Basin. Evaporite members were deposited in carbonate evaporite coastal sabkhas, and clastic members were deposited in mud-rich coastal to continental sabkhas that passed inland to wadi-plain environments.

Five distinct facies are recognized in the Eocene Queen City exposures between the Trinity River valley and the Louisiana state boundary. These facies (fluvial, deltaic, tidal flat, barrier, and tidal delta) display diagnostic suites of physical and biogenic structures. Sandstones within these facies exhibit substantial differences in paleocurrent pattern.

The Neogene Ogallala Formation is an alluvial apron that occurs east of the Rocky Mountains from South Dakota to the Southern High Plains of Texas. The Ogallala was deposited by coalescent, low-gradient, wet alluvial fans that headed in mountains to the west. Geometry and depositional facies of the Ogallala Formation in Texas north of the 33rd parallel have been determined from outcrop studies and drillers' log descriptions.