Original data
Where the ground itself cracks foundations: expansive clay by city
Some soil does not just hold water against a wall — it moves the wall. Expansive clay swells when it gets wet and shrinks as it dries, and that cycle heaves and cracks foundations from below. We used USDA soil-survey shrink-swell ratings to measure it for 197 US cities. In 40 of them, most of the sampled ground is high shrink-swell clay.
Garland, TX tops the list: 16 of 17 sampled points are high shrink-swell clay.
The pattern is geographic: the Texas metros, the Kansas–Missouri line, and the Colorado Front Range suburbs dominate the top of the list. This is why foundation repair — piers, underpinning — is such a large trade in those markets, and why it is a different problem from a wet basement.
Own a home on clay? The defense is moisture stability: keep the soil around the foundation from swinging between soaked and bone-dry. Consistent drainage, gutters that carry water away, and in drought even foundation watering all reduce the movement. Read the failure mode up close in our foundation repair cost guide.
Covering housing or construction? This is USDA shrink-swell data mapped to searchable cities, and it pairs with our water-table and freeze-thaw data: three independent ways the ground attacks a foundation, each from a public source.
Methodology and its one big limit
Source is USDA NRCS SSURGO via Soil Data Access. For each city we sampled 17 points around the centre and read linear extensibility (LEP) for the dominant soil component. A point counts as high shrink-swell when LEP is at least 6% in the top 100 cm — the threshold at which clay movement routinely damages foundations. We report how many of a city's LEP-rated points clear that bar.
The limit you must not ignore: LEP measures the soil. Where a city's expansive ground is deep claystone bedrockbelow the soil profile — Denver sitting on Pierre Shale is the classic case — this data reads low even though the foundation risk is real. A low score here is not a clean bill of health; it means the soil is not expansive, not that the ground beneath it isn't.
Cities with fewer than 5 LEP-rated points are left out, where a share would be one or two probes. This is soil-survey data, not a boring log of your lot.
Free to cite or reproduce with a link to this page. Download the full dataset (CSV) ↓
Cities ranked by expansive-clay exposure
99 cities where at least some sampled ground is high shrink-swell clay, ranked by the share of rated points that clear the threshold. A fuller bar means more of the ground moves with moisture.
Using this data
The method and its limit are above and the source is public, so the analysis is reproducible. Cite this page. Our water-table, freeze-thaw, flood claims, and permit fee datasets are alongside it.