County soil summary
Soil types in Multnomah County, Oregon
The most widespread soils are Zygore, Cascade and Aschoff; the most common drainage class is well drained (50% of the land), and typical topsoil pH is 5.8.
- Well or moderately well drained
- 61% of land · state 82%
- Typical topsoil pH
- 5.8 moderately acidic · state 6.7
- Septic fields very limited
- 85% of land · state 85%
- Subject to flooding
- 11% of land, any frequency · state 3%
Most common soils in Multnomah County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 56% of the mapped land; 114 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Urban landLand type, not a soil series | 13.3% | — | — |
| Zygore | 8.4% | Well drained | 5.8 |
| Cascade | 7.8% | Somewhat poorly drained | 5.6 |
| Aschoff | 6.1% | Well drained | 5.8 |
| Goble | 6.1% | Moderately well drained | 5.6 |
| Multnomah | 5.6% | Well drained | 5.8 |
| Sauvie | 5.2% | Poorly drained | 6.1 |
| Kinzel | 3.8% | Well drained | 5.0 |
What this means
What the soils in Multnomah County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Multnomah County is moderately acidic: pH 5.8 (most land between 5.3 and 6.1). Many vegetables grow well here, and some gardens benefit from a little lime. Test before adding any.
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 silt loam (38% of the land).
61% of the land is moderately well to excessively drained, which suits most garden plants.
For your lawn and yard
Most land is in hydrologic groups B and C, where rain soaks in at a moderate pace.
For a septic system
For conventional septic absorption fields, NRCS rates 85% of the land in Multnomah County very limited, 1% somewhat limited and 0% not limited (14% not rated, such as urban land, pits or water).
That is close to the state as a whole (85% very limited).
Where the soil is very limited (slow permeability, a high water table, flooding, shallow bedrock or steep slopes), alternative systems such as mound or sand-filter designs are common and cost more.
Flooding is mapped on 11% of the land (<1% occasional, 4% 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 (50%). 61% of the land is moderately well drained or better, compared with 82% across Oregon.
Show as a table
| Category | Multnomah County | Oregon |
|---|---|---|
| Excessively drained | 1.3% | 2.4% |
| Somewhat excessively drained | 3.2% | 4.8% |
| Well drained | 49.8% | 71.6% |
| Moderately well drained | 6.2% | 3.4% |
| Somewhat poorly drained | 11.8% | 2.4% |
| Poorly drained | 7.9% | 2.8% |
| Very poorly drained | 3.7% | 0.8% |
| Not rated | 16.1% | 11.8% |
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 | Multnomah County | Oregon |
|---|---|---|
| Not limited | 0.0% | 0.5% |
| Somewhat limited | 1.3% | 4.4% |
| Very limited | 84.9% | 85.3% |
| Not rated | 13.8% | 9.8% |
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 | Multnomah County | Oregon |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 10.8% | 10.0% |
| B: moderate infiltration | 34.6% | 16.7% |
| C: slow infiltration | 28.2% | 30.1% |
| D: very slow infiltration (clayey, shallow or wet) | 6.3% | 30.4% |
| A/D: D as is, A if drained | 0.0% | 0.3% |
| B/D: D as is, B if drained | 3.0% | 0.7% |
| C/D: D as is, C if drained | 3.4% | 2.4% |
| Not rated | 13.8% | 9.4% |
Flooding
Show as a table
| Category | Multnomah County | Oregon |
|---|---|---|
| No flooding | 88.4% | 80.8% |
| Rare or very rare | 7.0% | 1.4% |
| Occasional | 0.1% | 1.0% |
| Frequent or very frequent | 4.2% | 1.0% |
| Not reported | 0.2% | 15.9% |
Seasonal high water table
Show as a table
| Category | Multnomah County | Oregon |
|---|---|---|
| Within 18 inches at some time of year | 7.5% | 5.5% |
| 18 inches to 3.3 feet | 23.0% | 3.5% |
| Deeper than 3.3 feet or none reported | 69.5% | 75.5% |
| Not reported | 0.0% | 15.6% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 5.8 (moderately acidic); 80% of rated land falls between 5.3 and 6.1. Median topsoil organic matter is 5.5%.
Show as a table
| Category | Multnomah County | Oregon |
|---|---|---|
| Strongly acidic (below 5.5) | 9.5% | 10.4% |
| Moderately to slightly acidic (5.5–6.4) | 69.9% | 23.0% |
| Near neutral (6.5–7.3) | 2.8% | 40.4% |
| Alkaline (7.4 and up) | 0.0% | 13.8% |
| Not reported | 17.8% | 12.4% |
Texture
Show as a table
| Category | Multnomah County | Oregon |
|---|---|---|
| Sandy | 2.1% | 8.5% |
| Loamy (loam, silt loam and similar) | 69.4% | 77.3% |
| Clayey (40%+ clay) | 0.0% | 1.1% |
| Organic (muck or peat) | 0.1% | 0.4% |
| Not reported (rock, urban land, etc.) | 28.4% | 12.8% |
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
- Multnomah County, Oregon (FIPS 41051): 269,067 acres of mapped land, 28,590 acres of open water excluded. State comparisons pool all mapped land in Oregon.
- 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.