HOUSTON ARCHEOLOGICAL SOCIETY
SOUTHEAST TEXAS ARCHEOLOGY
REGIONAL GEOLOGY
Southeast Texas can be divided into two geological areas (Oetking 1959). From the Gulf coastline to about 80 miles inland, the surface geology is of Quaternary age, consisting of recent deposits, with Beaumont and then Lissie formations in stratified deeper deposits. From about 80 to 120 miles inland the surface geological deposits are of Tertiary age, with Pliocene, Miocene, and Oligocene deposits stratified in order of depth.
Most of the archeological excavations in Southeast Texas are done in
the first few feet from the soil surface in Pleistocene
materials that have been redeposited in the Holocene period, after 10,000
years ago. 
Holocene
period soils overlie older deposits, such as the Beaumont Formation. While
there seems to have been much changing of river channels near the coast
(Aten
1983a:Chapter 8), channels of smaller inland streams seem to have
been less subject to change. Many Indian sites along inland streams in
this region have long occupation sequences, from about the beginning of
the Holocene
period through the Late Prehistoric period. This implies stable stream
channels.
Holocene period soils in Southeast Texas are generally sandy, with verying amounts of clay and organic materials. Because of the uniformity of soil deposits at many site locations, natural soil stratigraphy is only occasionally useful as a relative time marker at archeological excavations. Of course, natural stratigraphy should be studied when present in a definite form, expecially as an indicator that undisturbed stratigraphy exists. Local depositional histories are usually difficult to determine at sites in this region. Therefore, a more detailed discussion of geology is unnecessary. It is common to see descriptions of regional geology in archeological site reports that are not used in any other portionof the text.
Aten (1983a:Chapter 11) has been able to identify the depositional histories of some coastal margin archeological sites, such as stream channel levee deposits and indications of marsh and floodplains. These types of data are useful in determining the site environment at the time of occupation. The placement of shell midden sites is usually apparent without geological indicators, however. This type of site was located at the edges of lakes and stream channels, wherever Rangia beds occurred. The relationship of depositional history to cultural factors of site formation is seldom considered in site reports, except as a chronological sequence, because cultural factors for formation processes of shell midden sites are not well understood.
At some sites in this region, there can be false indications of "A" horizon remnant paleosols, such as in Stratum 2 at site 41WH19 (Patterson et al. 1987). In this situation, dark lines are observed that have been apparently caused by leaching rather than being actual "A" horizons. The vertical distribution of soil particle size is occasionally used to study possible disturbance of natural stratigraphy (Ensore 1987).