Arizona: basement moisture and foundation risk by county
15 counties, ranked by our combined index. Highest combined risk is Coconino County (41), lowest is Graham County (27). The worst soil for foundation cracks specifically is in Santa Cruz County.
| County | Index | Moisture | Cracks | Water table | Region |
|---|---|---|---|---|---|
| Coconino County | 41 | 37 | 55 | 30 | Colorado Plateau |
| Apache County | 39 | 34 | 51 | 30 | Colorado Plateau |
| Cochise County | 36 | 31 | 47 | 30 | Basin and Range desert |
| Greenlee County | 36 | 29 | 50 | 30 | Basin and Range desert |
| Mohave County | 36 | 34 | 54 | 16 | Colorado Plateau |
| Pima County | 35 | 29 | 46 | 30 | Basin and Range desert |
| Pinal County | 35 | 29 | 46 | 30 | Basin and Range desert |
| Santa Cruz County | 35 | 29 | 57 | 16 | Basin and Range desert |
| Yuma County | 35 | 30 | 56 | 16 | Basin and Range desert |
| Navajo County | 34 | 31 | 29 | 46 | Rocky Mountains |
| Maricopa County | 33 | 30 | 50 | 16 | Basin and Range desert |
| Yavapai County | 33 | 29 | 40 | 30 | Rocky Mountains |
| Gila County | 29 | 29 | 29 | 30 | Rocky Mountains |
| La Paz County | 29 | 29 | 28 | 30 | Rocky Mountains |
| Graham County | 27 | 28 | 32 | 16 | Basin and Range desert |
Values from USDA NRCS SSURGO where available, otherwise our regional model — each county page states which. Methodology.
The physiographic regions inside Arizona
State lines are political; soil follows geology. These are the distinct ground types inside Arizona and why each behaves the way it does.
Basin and Range desert
Phoenix, Las Vegas, Tucson, Albuquerque. Rainfall is minimal and groundwater is deep, so seepage is not the story. Two other mechanisms are: expansive playa clays, and hydrocompactive fan soils that collapse the first time they are deeply wetted — typically by irrigation or a leaking service line rather than by rain.
8 counties: Cochise County, Graham County, Greenlee County, Maricopa County, Pima County, Pinal County, Santa Cruz County, Yuma County
Rocky Mountains
Shallow bedrock and coarse material. Basements are shallow or absent, and the problem is spring meltwater rather than a water table.
4 counties: Gila County, La Paz County, Navajo County, Yavapai County
Colorado Plateau
Arid, so groundwater is rarely the problem, but Mancos Shale is strongly expansive and some soils are also gypsiferous, which dissolves. Two mechanisms that both move a footing without any water reaching the basement.
3 counties: Apache County, Coconino County, Mohave County
Page data updated