The Quaternary section, from oldest to youngest is divided as follows: Willis, Gay Hill, Bastrop Park, Uvalde, Asylum, Capitol, Beaumont (Sixth Street), Live Oak Bar (approximately of Beaumont age), First Street, Riverview, and Sand Beach.
The section was divided with the assistance of a series of profiles constructed across the Coastal Plain, with initial work along Colorado River from Austin to the Gulf. The best marker horizon was found to be the top of the Uvalde. Uvalde and younger deposits contain limestone pebbles; in surface exposures older Pleistocene deposits are leached of all limestone content. Along Colorado River the two terrace deposits next younger than Uvalde, Asylum and Capitol, contain much granitic material. Southwestward there is change in facies and Asylum and Capitol deposits are largely clay and silt. Younger deposits—Beaumont (Sixth Street), First Street, Riverview, and Sand Beach—are silt-covered in the vicinity of Austin and beneath each silt cover limestone gravel commonly is present.
Source of gravel in the present streams is largely the older gravel deposits over or through which streams now are flowing. Gravel sizes in the stream beds decrease coastward as limestone is dissolved; and, besides material in solution, clay, silt, and fine sand are carried to the Gulf.
The Recent delta of Colorado River, which first appeared above water about 1910 and by 1936, had extended a distance of approximately 5 miles to connect the mainland with Matagorda offshore bar, suggests a similar relationship between Live Oak bar and deposits of Beaumont and younger age farther inland.
Late in the Pleistocene a blanket of caliche (Reynosa) formed west of the approximate 32-inch rainfall line or in the zone of pedocal (carbonate-accumulating) soils.
On the basis of stratigraphic position and leaching the Willis period of entrenchment and alluviation may be correlated with Nebraskan glacial and Aftonian interglacial ages, the Gay Hill, with the Kansan glacial and Yarmouth interglacial; the Bastrop Park, with the Illinoian glacial and Sangamon interglacial; and the Uvalde, with the Iowan and Peorian. The end of Beaumont time marks high sea-level, probably registering maximum retreat of Wisconsin ice.
The geologic picture of sedimentation during Quaternary time shows a series of coalescing deltas, each characterized by distinctive source material. The whole picture is complicated by coastward tilting, climatic changes, and a fluctuating sea-level.