States / Arizona
10 counties · median score 14
Crawl space moisture in Arizona
Most of Arizona drains well: only 0 of 10 counties score high or elevated, and the median is 14. Coconino County is the exception at 20; crawl-space moisture problems here usually come from grading, gutters and plumbing rather than the soil itself.
- 1Wettest county Coconino County
- 2High or elevated 0 of 10
- 3Median score 14
- 4Driest county Maricopa County
Arizona's soil, taken as a whole
Across the 23,239,311 acres mapped in these 10 counties, 0% of soil with a drainage class is somewhat poorly, poorly or very poorly drained, and 1% of acres report a seasonal water table within about two metres. That is a dry figure; wet soils here are confined to river bottoms and wetlands. 10 of the 10 counties have mapped soils subject to occasional or frequent flooding.
| Drainage class | Share of mapped acres |
|---|---|
| Excessively drained | 3% |
| Somewhat excessively drained | 11.8% |
| Well drained | 84.6% |
| Moderately well drained | 0.4% |
| Somewhat poorly drained | 0.1% |
| Poorly drained | 0.2% |
Radon. By EPA zone, 0 Arizona counties here are zone 1 (highest potential), 10 zone 2 and 0 zone 3. EPA says to test regardless of zone; a sealed crawl space is the cheapest moment to add radon venting if a test calls for it.
Every Arizona county
Sorted wettest first. High and elevated counties link to their own page with the full soil breakdown.
What drives the Arizona numbers
The wettest county, Coconino County, is 94% well drained by dominant condition, and sits in EPA radon zone 2. The driest, Maricopa County, is 77% well drained with no shallow water table reported. No Arizona county reaches the high tier.
The score is a guide to the soil, not to a house: a well-graded lot with working gutters in a high county can have a dry crawl space, and a bad downspout can flood one in a low county. The R408 calculator sizes venting or encapsulation for any footprint.
Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted; EPA Map of Radon Zones, county table (June 2024 JSON). Checked 2026-10-23.