Williamson County foundation soil map
How at-risk is your area, and what could it cost you? This map shows what your home likely sits on across WilCo — the expansive Blackland clay on the east side, the Edwards limestone on the west, and the transition band between them — with typical repair cost ranges for each zone. Zoom in, tap a city, or check your ZIP below.
Transition band (I-35 corridor) — moderate, varies street to street
Edwards limestone (west) — lower movement risk
Green outline = Williamson County service area
Permitted activity (sample) — Round Rock development permits; toggle layers with the control on the map
About the permitted activity layer (sample): points show City of Round Rock development permits from the city’s public GIS feed — Round Rock only for now. Not all repairs require a permit, and foundation repairs specifically often don’t, so this layer is indicative of construction activity against the soil zones, not a complete record. Only public, non-personal fields are shown. Use the layer control (top right of the map) to view soil only, permits only, or both.
Disclaimer: This map is a generalized view of the dominant soil pattern across Williamson County, drawn from the USDA soil survey mapping described under data sources below — it is 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.
Check your ZIP
General soil guidance based on Williamson County geology — not a site-specific survey. Lots vary, and cut-and-fill grading can change the picture on any street. An elevation survey and an engineer’s look confirm your specific home.
What repair typically costs in each zone
Statewide Texas figures for 2025 put slab repair at roughly $3,500–$7,000, pier-and-beam work at $6,000–$15,000, and severe structural cases at $20,000+. Where you sit on this map pushes you toward one end or the other, because pier depth — how far down stable material sits — is one of the two biggest cost drivers.
| Zone | Why it moves the price | Typical range |
|---|---|---|
| Blackland clay (east) | Piers must pass through deep active clay to reach stable material — deeper piers, often more of them. | Slab: toward the upper $3,500–$7,000 and beyond for multi-corner jobs. Pier-and-beam: $6,000–$15,000. Widespread movement: $20,000+. |
| Transition (I-35 corridor) | Depth to rock varies lot to lot, so quotes here spread the widest. Engineered fill in newer subdivisions adds variables. | Slab: the full $3,500–$7,000 band. Pier-and-beam: $6,000–$15,000. Severe cases: $20,000+. |
| Edwards limestone (west) | Stable rock sits shallow, so piers are shorter — when repair is needed at all, it skews cheaper. Problems are more often drainage or fill. | Slab: toward the lower $3,500–$7,000. Pier-and-beam: lower half of $6,000–$15,000. Severe cases are rarer. |
Williamson County ZIP codes by soil type
The same data the checker and map draw from, in full. Find your ZIP, then read what that zone actually means below.
| ZIP | Area | Dominant soil | Movement risk |
|---|---|---|---|
| 78634 | Hutto | Deep Blackland clay | Higher |
| 76574 | Taylor | Deep Blackland clay | Higher |
| 78660 | Pflugerville | Deep Blackland clay | Higher |
| 76537 | Jarrell | Blackland clay | Higher |
| 78615 | Coupland | Blackland clay | Higher |
| 78653 | Manor area | Blackland clay | Higher |
| 78664 | Round Rock (east/central) | Mixed clay and limestone | Moderate |
| 78665 | Round Rock (north) | Mixed clay and limestone | Moderate |
| 78681 | Round Rock (west) | Mixed, trending rockier | Moderate |
| 78626 | Georgetown (east/central) | Mixed clay and limestone | Moderate |
| 78628 | Georgetown (west) | Mixed, trending rockier | Moderate |
| 78633 | Georgetown / Sun City | Mixed clay and limestone | Moderate |
| 78613 | Cedar Park | Edwards limestone | Lower |
| 78641 | Leander | Edwards limestone | Lower |
| 78645 | Leander / northwest | Edwards limestone | Lower |
| 78642 | Liberty Hill | Edwards limestone | Lower |
| 78717 | NW Austin / Avery Ranch | Edwards limestone | Lower |
What each zone means for your house
Higher risk — deep Blackland clay (east of I-35)
Houston Black clay has a high plasticity index, which is the technical way of saying it swells a lot when wet and shrinks hard when dry. Under a slab that movement is uneven — more at the exposed edges, less under the protected centre — so the slab flexes. Hutto, Taylor and the fast-growing flatlands around the Samsung plant sit squarely on it. Seasonal cracks and doors that stick by August are common here and often correct partway after the rains. Consistent moisture and good drainage genuinely help; a pattern of damage is worth an engineer’s look. There’s a deeper explainer on why east-county homes crack more.
Moderate — the transition zone (Round Rock, Georgetown)
This is the messiest zone to generalise about, because the clay-to-rock boundary runs straight through it. Two houses a few streets apart can behave differently, and newer subdivisions add engineered fill on top of whatever was there. Sun City and Wolf Ranch in Georgetown, and Teravista and Forest Creek in Round Rock, all sit in this band. Movement happens but is usually milder than east county. An elevation survey is what tells you which situation your specific lot is in.
Lower — nearer the Edwards limestone (west county)
Along the Balcones Escarpment the ground turns rocky and barely moves. Cedar Park, Leander and Liberty Hill sit here. Foundation problems in west county are more often about lot grading, drainage, or poorly compacted fill than deep soil swelling — and piers can be shallower because stable rock is closer, which sometimes makes repair cheaper. If you’re seeing movement on limestone, water is the first thing a good crew should check.
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.
If you are already seeing cracks, the crack checker walks them past what a Texas engineer actually looks at, and the watering advisor covers keeping moisture steady without breaking your provider’s restrictions.
Common questions
Does my ZIP code decide whether my foundation will crack?
No — it sets the odds, not the outcome. Drainage, the age of the house, how the lot was graded, under-slab plumbing leaks and tree placement all matter. Plenty of Hutto homes on the worst clay never have a problem because the water is managed well.
My street is on the boundary. What then?
Assume the more active soil until an elevation survey says otherwise. The transition isn’t a clean line on the ground, and cut-and-fill grading can put clay fill on a limestone lot.
Does the soil change what repair costs?
It changes pier depth, which is one of the two biggest cost drivers. Piers have to reach stable soil — shallow over the Austin Chalk, much deeper through east-county clay. The zone table above shows how that shifts the typical 2025 ranges, and the cost guide breaks a real quote down line by line.
Data sources
The soil zones on this map are a generalization of the official county soil mapping: the USDA Web Soil Survey (SSURGO database, Soil Survey of Williamson County, Texas), which maps the eastern county as Blackland Prairie clays — Houston Black, Heiden and Branyon series, all rated high shrink-swell — and the western county as shallow soils over Edwards limestone and Austin Chalk (Eckrant, Doss and Brackett series, low shrink-swell), with mixed units along the I-35 corridor. County GIS soil layers published for the Austin region reflect the same SSURGO mapping. The permitted-activity layer pulls City of Round Rock development-permit records live from the city’s public ArcGIS REST feed listed on the Round Rock GeoHub (only public, non-personal fields are displayed; not all repairs require a permit, so it is a sample of activity, not a complete record). Cost figures are typical 2025 Texas foundation repair ranges; see the cost guide for how an individual quote is actually built. This page is general information, not engineering advice.
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.
Get a local crew’s read on your foundation
Whatever the map shows, an on-site look is what tells you what’s really happening. We’ll match you with up to three independent local contractors — free, no obligation.
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