Low risk About 0% of San Juan County's soil area is high shrink-swell (expansive) clay — far below the Washington average of 1%, and far below the national average of 17%. That places it #28 of 33 Washington counties for foundation soil risk.
Share of the county's ~114,882 acres of USDA-mapped soil with linear extensibility ≥ 6% in the top meter (SSURGO).
| High shrink-swell (expansive) clay | 0% |
| Moderately expansive | 28% |
| Low / non-expansive | 72% |
| Foundation risk tier | Low |
| Rank in Washington | #28 of 33 counties |
| Higher-risk than | 0% of all U.S. counties |
Expansive clay swells as it takes on water and shrinks as it dries, and that repeated movement is what lifts and drops a foundation unevenly — opening stair-step cracks, racking door and window frames, and, left unmanaged, cracking slabs and footings. San Juan County's exposure is minimal. With just 0% high-expansive soil, expansive clay is unlikely to be the main driver of foundation movement in San Juan County. Settlement here more often traces to drainage, fill, tree roots, or original construction — worth a diagnosis before paying for clay fixes.
| County | High-risk soil | |
|---|---|---|
| Higher risk → | Island County | 0% |
| This county | San Juan County (#28 of 33) | 0% |
| Lower risk → | Benton County | 0% |
For context, the average Washington county is 1% high-expansive soil and the average U.S. county is 17%.
Foundation problems get more expensive the longer they wait. Get an assessment and repair quotes from independent local pros.
Get repair quotes →Costs follow the same structure everywhere — from a few hundred dollars for a single crack injection to $8,000–$25,000+ for pier stabilization on a settling home. At this risk level the clay is rarely the culprit, so a proper diagnosis is the first dollar to spend. See the full foundation repair cost guide for method-by-method pricing.
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.