formations are exposed in the north (Polk, San Jacinto, and Tyler counties), while the more recent Quaternary Period formations are exposed in the south (Hardin and Liberty counties).

Soils: The soils of the various formations at the surface have shifted and intermingled through erosion and other factors over time and can be locally quite complex. The Big Thicket contains a greater variety of soils than any area of comparable size in the United States. Sources vary,