High risk About 20% of Union County's soil area is high shrink-swell (expansive) clay — 1.3 times the New Mexico average of 16%, and above the national average of 17%. That places it #8 of 23 New Mexico counties for foundation soil risk.
Share of the county's ~2,450,060 acres of USDA-mapped soil with linear extensibility ≥ 6% in the top meter (SSURGO).
| High shrink-swell (expansive) clay | 20% |
| Moderately expansive | 40% |
| Low / non-expansive | 40% |
| Foundation risk tier | High |
| Rank in New Mexico | #8 of 23 counties |
| Higher-risk than | 68% 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. Union County's exposure is high. In a county this exposed, water management is the highest-leverage thing a Union County homeowner controls: gutters and downspouts that carry roof water well clear of the slab, positive grading away from the house, and — most of all — consistent soil moisture through drought, because it is the wet-to-dry swing that cracks a foundation, not moisture itself.
Union County's shrink-swell risk is concentrated in the Torreon soil series alongside La Brier and Carnero — clays the USDA maps as strongly expansive, swelling and shrinking with every wet–dry cycle. Homes built on these series most need the drainage and moisture discipline above; a lot-level soil report (or the county NRCS survey) shows which one sits under a given address.
| County | High-risk soil | |
|---|---|---|
| Higher risk → | San Miguel County | 24.6% |
| This county | Union County (#8 of 23) | 19.7% |
| Lower risk → | Sierra County | 17.5% |
For context, the average New Mexico county is 16% 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.
How to 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. Because expansive clay drives recurring, moisture-linked movement here, correcting drainage first often heads off a far larger repair later. 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.