Late Pleistocene Delta
This region is exposed Beaumont formation material that was likely deposited in a delta during the Late Pleistocene (126,000 to 10,000 years ago). The Beaumont formation in this area is made of mostly clay, silt, sand, and gravel representing stream channels, point bars, natural levees, and backswamp deposits. Massive accumulations of calcium carbonate (caliche) and concentrations of iron-manganese oxides are common in the zone of weathering.
Four subcategories of Beaumont are recognized within this area. The labels Qbr and Qbs represent areas made of sand and silt. Qbc represents areas made of clay, mud, and silt. These are floodplain deposits that exist between the channels. Qbc represents areas made of clay, mud, and silt. These are channel deposits with sandier material found along the channel banks.
Reference: Barnes, V.E. 1976. Geologic Atlas of Texas, McAllen-Brownsville Sheet. The University of Texas Bureau of Economic Geology, Map.