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 ~114,900 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 |
Figures are rounded — components may not sum to exactly 100%.
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 → | Mason County | 0.5% |
| This county | San Juan County (#28 of 33) | 0.0% |
For context, the average Washington county is 1% high-expansive soil and the average U.S. county is 17%.
Foundation repair is one of the most over-sold jobs in home services — quotes for the same house can vary 3×. Before you sign anything, learn how to get honest bids and what a fair price looks like.
Before you call a foundation company →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.
Data current as of July 2026 — soil risk from USDA SSURGO; repair cost ranges reviewed for 2026.
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.