Crawl space moisture in Coconino County, AZ

73% of Coconino County's soil falls in hydrologic group D or a dual D group: clays and high water tables that shed water slowly. No shallow seasonal water table is reported.

Size venting or encapsulation

1Water table deep
2Wet soils 0%
3Moisture score 20
4EPA radon zone 2

Share of mapped soil acres in Coconino County, AZ by NRCS drainage class (dominant condition), bars to scale; wetter classes highlighted. Covers 98% of mapped acres.

Dominant drainage

Well drained

94% of acres

Group D soils

73%

slow infiltration

Flood-prone acres

any flooding frequency

Ponding

acres where water ponds

Reading the Coconino County soil survey

The score of 20 combines four parts, each from the USDA survey: wet drainage classes contribute 0.1 points of 100 on their own scale, group D soils 78.6, a shallow water table 0, and flooding 1; the weights are on the methodology page. The dominant hydrologic group is D (73% of acres): very slow infiltration, high runoff (clays, high water table).

Hydrologic soil groups in Coconino County by share of acres, columns to scale. Group D and dual groups (x/D) shed water slowly and hold it near the surface.

Coconino County against the rest of Arizona

Coconino County ranks 1 of 10 Arizona counties, 6 points above the state median of 14. Only no other county in the state scores higher. Statewide, 0% of mapped soil is in the wet drainage classes; here it is 0%. After well drained, the next most common class is somewhat excessively drained at 3%.

Flooding. 0.1% of acres with a flooding class are rated frequent; 0.4% of acres with a flooding class are rated occasional; 3.7% of acres with a flooding class are rated rare; 0% of acres with a flooding class are rated very rare. Flood-prone soils are a minority here, concentrated along streams; the score mostly reflects what happens between floods.

What it means for a crawl space here

In a moderate county the soil record is mixed rather than uniformly wet, so conditions vary from lot to lot. Where the lot drains, the model-code default — a vented crawl space with 1 sq ft of net vent per 150 sq ft of floor, or 1 per 1500 with a Class I vapor retarder on the ground — is a reasonable starting point; where the sections above point to a shallow water table or flood-prone soil on your lot, plan as for an elevated county. Either way, check the site first: grading that falls away from the foundation, gutters and downspouts that discharge well clear of it, and a ground cover over bare earth. A wet crawl space in a moderate county points to one of those first.

Radon. EPA radon zone 2. The zone is a county-level prediction; EPA says elevated levels occur in every zone and every home should be tested.

Near Coconino County by score

Graham County 17Navajo County 16Yavapai County 16Cochise County 14

All 10 Arizona counties

Sources: USDA NRCS SSURGO via Soil Data Access (muaggatt: drclassdcd, hydgrpdcd, flodfreqdcd, pondfreqprs, wtdepannmin), acreage-weighted (survey areas AZ629, AZ631; drainage covers 98% of 3,221,816 mapped acres); EPA Map of Radon Zones, county table (June 2024 JSON); IRC R408.3 Unvented crawl space, as adopted in S.C. Code Regs. 8-1221 (LII). Checked 2026-10-23.