Gumbo clay never stops the wheel, but a wet week stops the truck
Harris County's working soil is the Lake Charles series, classified by USDA-NRCS as fine, smectitic, hyperthermic Typic Hapluderts, formed in clayey deposits of the Pleistocene Beaumont Formation. Fort Bend sits largely on Bernard, saturated within 0.6 meters of the surface in winter and early spring; groundwater beneath both is regulated by the Harris-Galveston Subsidence District, created in 1975 to end subsidence.
Lake Charles opens surface cracks 1 to 5 centimeters wide and over 30 centimeters deep that stay open 60 to 90 cumulative days a year, so a dry summer leaves a fissured yard and a loosened root plate. Permeability is very slow, so a grind hole holds water for days and smectitic backfill swells and shrinks seasonally instead of settling once. Both series run past 200 centimeters of clay and never reach a lithic contact: no rock, no refusal, depth set by the machine rather than by stone, the opposite of Austin's limestone.
That clay is also why storms here leave craters rather than stumps: saturated clay loses shear strength as wind loading peaks, and shallow-rooted species go over. USDA Forest Service Silvics calls loblolly lateral roots "prominent in a superficial system" on poorly drained sites. A tipped root plate is dirtier than a cut stump and the crater needs fill. Access, not hardness, is the limiter.