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Interactive · San Antonio ↔ Austin corridor

The Central Texas Foundation Soil Map

One fault line — the Balcones Escarpment — decides how the ground under your house behaves. East of it: deep, reactive Blackland clay that heaves and shrinks by inches a year. West of it: thin soil over Edwards limestone. Tap your city to see which world you're in.

EDWARDS PLATEAU · limestone BLACKLAND PRAIRIE · expansive clay ◤ BALCONES ESCARPMENT San AntonioAustin
Blackland clay — high shrink–swell Escarpment transition — variable Edwards limestone — lower swell
Why the line matters

Two soil worlds, one metro area

The San Antonio–Austin corridor runs straight along the Balcones Escarpment, the geologic seam that splits Central Texas in two. It isn't a subtle gradient — a foundation approach that's right on one side can be exactly wrong a mile away on the other.

East & south

Blackland Prairie clay

Deep, dark, high-plasticity Vertisols — Houston Black is the classic series, with plasticity indices commonly 40–60. It swells hard when the rains return and cracks open in drought. That seasonal shrink–swell is the number-one driver of foundation distress across the corridor, and why steel piers driven past the active zone are the durable fix.

West & north (Hill Country)

Edwards Plateau limestone

Thin residual soils over fractured limestone. Much less shrink–swell — but shallow bedrock, solution cavities, and imported fill create differential-bearing problems of their own. A measured elevation survey tells the real story lot by lot.

The catch

Straddle lots are the hardest of all

Right on the escarpment — much of New Braunfels, San Marcos, Round Rock, Georgetown and the north edge of San Antonio — a single property can sit on deep clay at one corner and shallow rock at another. That mismatch causes differential movement no ZIP-code rule of thumb can predict. It's exactly where a free, ±0.01-inch elevation survey earns its keep.

Full city index

Foundation repair by city & soil type

Every location GroundLock serves, grouped by its soil province. Open your city for local soil detail, typical repair scope, and a free elevation survey.

Blackland clayHigh shrink–swell
Escarpment transitionMixed / variable
Edwards limestoneLower swell · bearing/cavity

Soil provinces are generalized from established Central-Texas geology (the Balcones fault zone dividing the Blackland Prairie from the Edwards Plateau) and USDA soil-series behavior. Conditions vary lot by lot — verify your address with the free USDA Web Soil Survey or a site-specific geotechnical report before making foundation decisions.

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