County soil summary
Soil types in Maricopa County, Arizona
The most widespread soils are Gunsight, Rillito and Gilman; the most common drainage class is well drained (51% of the land), and typical topsoil pH is 8.2.
- Well or moderately well drained
- 83% of land · state 81%
- Typical topsoil pH
- 8.2 moderately alkaline · state 7.9
- Septic fields very limited
- 47% of land · state 62%
- Subject to flooding
- 11% of land, any frequency · state 9%
Most common soils in Maricopa County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 41% of the mapped land; 116 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Unnamed soilsGeneral soil group, not a named series | 9.9% | — | — |
| Rock outcropLand type, not a soil series | 5.4% | — | — |
| Gunsight | 5.0% | Somewhat excessively drained | 8.2 |
| Rillito | 4.8% | Somewhat excessively drained | 8.2 |
| Gilman | 4.3% | Well drained | 8.2 |
| Denure | 3.9% | Somewhat excessively drained | 8.0 |
| Carrizo | 3.9% | Excessively drained | 7.9 |
| Mohall | 3.7% | Well drained | 8.2 |
What this means
What the soils in Maricopa County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Maricopa County is moderately alkaline: pH 8.2 (most land between 7.9 and 8.5). Acid-loving plants such as blueberries and azaleas struggle without amended beds, and some trees and shrubs show iron chlorosis (yellow leaves with green veins).
Loamy topsoil (loam, silt loam and similar) covers 69% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is loam (12% of the land).
33% of the land is excessively or somewhat excessively drained: water moves through fast, so gardens need more frequent watering in dry spells.
For your lawn and yard
29% of the land is in hydrologic group A, where water soaks in fast. Lawns there dry out quickly; deeper, less frequent watering and organic matter help.
For a septic system
For conventional septic absorption fields, NRCS rates 47% of the land in Maricopa County very limited, 15% somewhat limited and 21% not limited (17% not rated, such as urban land, pits or water).
Statewide, 62% of the land is very limited, so Maricopa County is less restrictive than typical.
Flooding is mapped on 11% of the land (8% occasional, <1% frequent).
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Drainage
How long the soil stays wet
The most common drainage class is well drained (51%). 83% of the land is moderately well drained or better, compared with 81% across Arizona.
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| Excessively drained | 4.9% | 5.5% |
| Somewhat excessively drained | 27.7% | 12.3% |
| Well drained | 50.8% | 62.5% |
| Moderately well drained | 0.0% | 0.8% |
| Somewhat poorly drained | 0.0% | 0.3% |
| Poorly drained | 0.0% | 0.1% |
| Very poorly drained | 0.0% | 0.0% |
| Not rated | 16.6% | 18.4% |
Septic absorption fields
NRCS rating for conventional drain fields
The rating looks at the soil from 24 to 60 inches deep: permeability, depth to a seasonal water table or bedrock, flooding and slope. “Very limited” means at least one feature is unfavorable enough that a conventional field is hard to make work.
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| Not limited | 20.9% | 8.6% |
| Somewhat limited | 15.2% | 9.6% |
| Very limited | 47.3% | 62.0% |
| Not rated | 16.6% | 19.7% |
Rain, runoff and water table
Hydrologic soil group, flooding, seasonal water table
Hydrologic soil group
How fast rain soaks in when the soil is already wet. Group A soaks in fastest, D slowest.
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 28.8% | 17.2% |
| B: moderate infiltration | 16.0% | 10.3% |
| C: slow infiltration | 21.6% | 23.3% |
| D: very slow infiltration (clayey, shallow or wet) | 20.6% | 36.0% |
| A/D: D as is, A if drained | 0.0% | 0.0% |
| B/D: D as is, B if drained | 0.0% | 0.0% |
| C/D: D as is, C if drained | 0.0% | 0.0% |
| Not rated | 12.9% | 13.3% |
Flooding
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| No flooding | 79.4% | 79.9% |
| Rare or very rare | 1.7% | 4.4% |
| Occasional | 8.4% | 4.0% |
| Frequent or very frequent | 0.5% | 0.9% |
| Not reported | 9.9% | 10.8% |
Seasonal high water table
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| Within 18 inches at some time of year | 0.4% | 0.1% |
| 18 inches to 3.3 feet | 0.0% | 0.5% |
| Deeper than 3.3 feet or none reported | 89.6% | 88.6% |
| Not reported | 9.9% | 10.8% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 8.2 (moderately alkaline); 80% of rated land falls between 7.9 and 8.5. Median topsoil organic matter is 0.4%.
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| Strongly acidic (below 5.5) | 0.0% | 0.0% |
| Moderately to slightly acidic (5.5–6.4) | 0.0% | 3.6% |
| Near neutral (6.5–7.3) | 0.1% | 19.2% |
| Alkaline (7.4 and up) | 83.3% | 57.2% |
| Not reported | 16.6% | 20.0% |
Texture
Show as a table
| Category | Maricopa County | Arizona |
|---|---|---|
| Sandy | 13.3% | 13.4% |
| Loamy (loam, silt loam and similar) | 69.2% | 64.7% |
| Clayey (40%+ clay) | 0.9% | 1.8% |
| Organic (muck or peat) | 0.0% | 0.0% |
| Not reported (rock, urban land, etc.) | 16.6% | 20.1% |
Sources & data dates
- Source
- USDA NRCS Soil Survey Geographic Database (SSURGO), queried through Soil Data Access. Public domain.
- Data date
- SSURGO as published on November 3, 2026 (most recent survey area update October 26, 2026). NRCS refreshes SSURGO each October.
- Scope
- Maricopa County, Arizona (FIPS 04013): 6,231,260 acres of mapped land, 2,031 acres of open water excluded. State comparisons pool all mapped land in Arizona.
- Method
- Shares are by mapped land area: each map unit’s acres in the county times each soil component’s percentage. Open water is excluded. Topsoil values use the first mineral horizon of each component. Full methodology.