Williamson County foundation soil map

A general look at what your home likely sits on across WilCo — the expansive Blackland clay on the east side, the Edwards limestone on the west — and why it decides how much your foundation moves. Zoom in to your area.

Disclaimer: This map shows the general, most common soil trend across Williamson County — not a site-specific survey. The real boundary between clay and limestone is gradual and irregular, and any individual lot can differ from the area around it (cut-and-fill grading, pockets of one soil inside the other, and creek bottoms all change the picture). Your home’s actual soil is confirmed by an elevation survey and a geotechnical or structural engineer, not by this map. Base map © OpenStreetMap contributors.

What the two sides mean for your foundation

East of roughly the I-35 corridor — Hutto, Taylor, Pflugerville, and much of Round Rock and Georgetown — homes sit on deep Blackland Prairie clay that swells when wet and shrinks hard in a drought. That seasonal movement is the main driver of slab cracking here. West toward Cedar Park, Leander, and Liberty Hill, the ground trends to Edwards limestone, which barely moves — so foundation problems there are more often about lot grading, drainage, or engineered fill. There’s a full explainer on why east-county homes crack more, and you can check your soil risk by ZIP.

Where the boundary actually runs

The dividing line is the Balcones Escarpment, and it runs roughly north-south through the middle of the county, close to the I-35 corridor. It is a geological fault zone, not a neat line on a map, and that matters for anyone near it.

East of it lies the Blackland Prairie: deep Houston Black clay laid down over ancient seabed, with a high plasticity index. It swells when it rains and shrinks hard in a drought, and it does so unevenly under a house — more at the exposed slab edge, less under the protected middle. Hutto, Taylor, Coupland and the flatlands filling in around the Samsung plant sit here.

West of it the ground rises into Edwards limestone and the weathered Austin Chalk beneath. Rock does not shrink and swell, so foundations move far less. Cedar Park, Leander and Liberty Hill sit on this side, and piers there often reach stable material sooner — which can make repair cheaper when it is needed at all.

The transition band through Round Rock and Georgetown is the tricky part. Two houses a few streets apart can sit on different material, and newer subdivisions bring engineered fill that changes the picture again. Sun City and Wolf Ranch in Georgetown, Teravista and Forest Creek in Round Rock, all fall in this band. In the transition zone, a countywide generalisation is worth very little and an elevation survey is worth a lot.

What this map can and can’t tell you

It shows the regional pattern, which is genuinely useful for understanding why your neighbourhood behaves the way it does. It cannot tell you what is under one specific lot. Cut-and-fill grading routinely moves soil around during development, drainage varies house to house, and a plumbing leak under a slab creates movement that has nothing to do with the regional geology. Treat this as context, not a survey.

For a quicker read, the soil-risk ZIP checker lists every Williamson County ZIP and its dominant soil. If you are already seeing cracks, the crack checker walks them past what a Texas engineer actually looks at.

Foundation repair by city

Soil, neighborhoods and permit rules differ across the county. Local detail for Round Rock, Georgetown, Cedar Park, Leander, Hutto, Pflugerville and Taylor, or see every area we serve.

Use this map on your own site? You’re welcome to link to this page or embed a link back to it — a credit to Wilco Foundation Quotes is appreciated.