43 counties mapped. On average, 22% of Montana county soil area is high shrink-swell clay (USDA SSURGO).
Higher percentages mean more of a county's mapped soil is shrink-swell clay that expands and contracts with moisture. This is county-scale exposure, not a diagnosis of any single home — but it tells you whether soil movement belongs on your radar.
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Before you call a foundation company →| County | Tier | High-risk % | Moderate % |
|---|---|---|---|
| Phillips | Severe | 60% | 31% |
| Petroleum | Severe | 57% | 18% |
| Fergus | Severe | 55% | 18% |
| Valley | Severe | 51% | 38% |
| Carter | Severe | 49% | 26% |
| Big Horn | Severe | 44% | 29% |
| Treasure | Severe | 43% | 22% |
| Chouteau | Severe | 38% | 47% |
| Cascade | Severe | 35% | 29% |
| Liberty | Severe | 34% | 57% |
| Yellowstone | Severe | 33% | 27% |
| Carbon | Severe | 31% | 30% |
| Toole | High | 29% | 62% |
| Hill | High | 29% | 60% |
| Stillwater | High | 26% | 44% |
| Golden Valley | High | 26% | 25% |
| Musselshell | High | 25% | 39% |
| Park | High | 24% | 31% |
| Custer | High | 22% | 26% |
| Sweet Grass | High | 21% | 39% |
| Fallon | High | 21% | 31% |
| Garfield | High | 20% | 26% |
| Wibaux | High | 20% | 37% |
| Red Rock Lakes Area - Part of Beaverhead | Moderate | 14% | 29% |
| Granite | Moderate | 13% | 26% |
| Wheatland | Moderate | 13% | 33% |
| Gallatin | Moderate | 12% | 32% |
| Horse Prairie-South Valley Area - Part of Beaverhead | Moderate | 12% | 38% |
| Powell | Moderate | 12% | 34% |
| McCone | Moderate | 12% | 56% |
| Lewis and Clark | Moderate | 10% | 38% |
| Meagher | Moderate | 10% | 34% |
| Big Hole Area - Part of Beaverhead | Moderate | 10% | 56% |
| Prairie | Moderate | 9% | 25% |
| Dawson | Moderate | 8% | 41% |
| Richland | Moderate | 7% | 58% |
| Sheridan | Moderate | 6% | 67% |
| Deer Lodge | Low | 3% | 27% |
| Madison | Low | 2% | 25% |
| Missoula | Low | 2% | 10% |
| Broadwater | Low | 2% | 21% |
| Lake | Low | 1% | 22% |
| Dillon Area - Part of Beaverhead | Low | 0% | 35% |
Risk metrics are computed from USDA SSURGO soil survey data (linear extensibility of soil components, area-weighted by county). Soil varies lot to lot — this is county-scale context, not a substitute for a site-specific geotechnical or structural assessment.