Expansive Soil in New Mexico: County Ratings
6 of the 33 rated counties in New Mexico have a dominant shrink-swell rating of High or Very High. Each rating below is the NRCS shrink-swell class covering the largest share of the county's mapped soil acres, computed from USDA SSURGO data. Open a county for the full class breakdown and what it means for a slab foundation.
| County | Dominant class | High + Very High share | Survey coverage |
|---|---|---|---|
| Bernalillo County | Low | 11% | 98% |
| Catron County | Moderate | 32% | 100% |
| Chaves County | Low | 3% | 100% |
| Cibola County | High | 54% | 96% |
| Colfax County | High | 50% | 100% |
| Curry County | Moderate | 25% | 100% |
| De Baca County | Low | 2% | 100% |
| Dona Ana County | Low | 1% | 100% |
| Eddy County | Low | 3% | 95% |
| Grant County | High | 59% | 100% |
| Guadalupe County | Moderate | 1% | 100% |
| Harding County | Low | 16% | 91% |
| Hidalgo County | High | 47% | 84% |
| Lea County | Moderate | 1% | 100% |
| Lincoln County | Low | 4% | 100% |
| Los Alamos County | High | 50% | 75% * |
| Luna County | Low | 32% | 100% |
| McKinley County | Moderate | 37% | 99% |
| Mora County | High | 61% | 100% |
| Otero County | Low | 5% | 99% |
| Quay County | Low | 13% | 100% |
| Rio Arriba County | Moderate | 16% | 99% |
| Roosevelt County | Moderate | 1% | 100% |
| San Juan County | Low | 3% | 98% |
| San Miguel County | Low | 20% | 98% |
| Sandoval County | Moderate | 9% | 97% |
| Santa Fe County | Moderate | 10% | 100% |
| Sierra County | Low | 22% | 99% |
| Socorro County | Low | 5% | 99% |
| Taos County | Low | 9% | 99% |
| Torrance County | Moderate | 5% | 100% |
| Union County | Low | 20% | 100% |
| Valencia County | Low | 8% | 97% |
* Less than 80% of this county's map acres have completed soil survey data; treat its rating as provisional.
How these ratings are computed
Ratings come from USDA NRCS SSURGO soil survey data: for each soil component we take the maximum linear extensibility percent (lep_r) in the top 100 cm, apply the NRCS Handbook Part 618 class limits (Low under 3 percent, Moderate 3 to 6, High 6 to 9, Very High 9 and above), assign map units by plurality of component percent, and roll acres up to the county. Full details on the methodology section of the lookup page. A county rating is not a parcel-level geotechnical assessment.