Expansive Soil in Arizona: County Ratings
2 of the 14 rated counties in Arizona 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 |
|---|---|---|---|
| Apache County | Low | 9% | 93% |
| Cochise County | Low | 32% | 98% |
| Coconino County | Low | 22% | 90% |
| Gila County | Low | 43% | 92% |
| Graham County | High | 50% | 97% |
| Greenlee County | High | 52% | 88% |
| La Paz County | Low | 2% | 99% |
| Maricopa County | Low | 4% | 98% |
| Mohave County | Low | 10% | 91% |
| Navajo County | Low | 10% | 93% |
| Pima County | Low | 8% | 98% |
| Pinal County | Low | 21% | 99% |
| Yavapai County | Low | 38% | 88% |
| Yuma County | Low | 3% | 99% |
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.