County soil summary
Soil types in Gallatin County, Montana
The most widespread soils are Brocko; the most common drainage class is well drained (69% of the land), and typical topsoil pH is 7.0.
- Well or moderately well drained
- 78% of land · state 86%
- Typical topsoil pH
- 7.0 neutral · state 7.2
- Septic fields very limited
- 67% of land · state 78%
- Subject to flooding
- 5% of land, any frequency · state 4%
Most common soils in Gallatin County
Share of mapped land
A county is a patchwork of many soils. These 8 cover 41% of the mapped land; 168 named soil series are mapped here in all.
| Soil | Share of land | Drainage | Topsoil pH |
|---|---|---|---|
| Typic CryochreptsGeneral soil group, not a named series | 9.0% | — | — |
| Rock outcropLand type, not a soil series | 7.0% | — | — |
| Mollic CryoboralfsGeneral soil group, not a named series | 6.5% | — | — |
| Typic CryoboralfsGeneral soil group, not a named series | 6.2% | — | — |
| Argic CryoborollsGeneral soil group, not a named series | 5.2% | — | — |
| Other soilsGeneral soil group, not a named series | 2.6% | — | — |
| Brocko | 2.5% | Well drained | 7.9 |
| Dystric CryochreptsGeneral soil group, not a named series | 2.3% | — | — |
What this means
What the soils in Gallatin County mean for gardens, lawns and septic systems
For your garden
Typical topsoil in Gallatin County is neutral: pH 7.0 (most land between 5.6 and 7.9), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 85% of the land: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is loam (21% of the land).
78% 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 67% of the land in Gallatin County very limited, 19% somewhat limited and 1% not limited (14% not rated, such as urban land, pits or water).
Statewide, 78% of the land is very limited, so Gallatin County is less restrictive than typical.
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 5% of the land (<1% 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 (69%). 78% of the land is moderately well drained or better, compared with 86% across Montana.
Show as a table
| Category | Gallatin County | Montana |
|---|---|---|
| Excessively drained | 0.9% | 1.9% |
| Somewhat excessively drained | 8.8% | 3.8% |
| Well drained | 68.6% | 79.4% |
| Moderately well drained | 0.1% | 1.2% |
| Somewhat poorly drained | 4.6% | 0.9% |
| Poorly drained | 2.0% | 1.0% |
| Very poorly drained | 1.3% | 0.6% |
| Not rated | 13.8% | 11.2% |
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 | Gallatin County | Montana |
|---|---|---|
| Not limited | 1.0% | 2.9% |
| Somewhat limited | 18.6% | 9.5% |
| Very limited | 66.6% | 78.4% |
| Not rated | 13.8% | 9.1% |
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 | Gallatin County | Montana |
|---|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 7.7% | 7.1% |
| B: moderate infiltration | 38.0% | 25.2% |
| C: slow infiltration | 31.0% | 34.9% |
| D: very slow infiltration (clayey, shallow or wet) | 14.7% | 27.5% |
| A/D: D as is, A if drained | 0.0% | 0.2% |
| B/D: D as is, B if drained | 2.3% | 0.5% |
| C/D: D as is, C if drained | 1.0% | 0.6% |
| Not rated | 5.2% | 3.9% |
Flooding
Show as a table
| Category | Gallatin County | Montana |
|---|---|---|
| No flooding | 81.1% | 85.4% |
| Rare or very rare | 4.0% | 2.1% |
| Occasional | 0.8% | 1.6% |
| Frequent or very frequent | 0.3% | 0.6% |
| Not reported | 13.7% | 10.3% |
Seasonal high water table
Show as a table
| Category | Gallatin County | Montana |
|---|---|---|
| Within 18 inches at some time of year | 3.3% | 1.5% |
| 18 inches to 3.3 feet | 4.7% | 1.0% |
| Deeper than 3.3 feet or none reported | 78.8% | 87.7% |
| Not reported | 13.2% | 9.8% |
Topsoil pH and texture
First mineral layer of each soil
Typical topsoil pH is 7.0 (neutral); 80% of rated land falls between 5.6 and 7.9. Median topsoil organic matter is 3%.
Show as a table
| Category | Gallatin County | Montana |
|---|---|---|
| Strongly acidic (below 5.5) | 4.2% | 2.5% |
| Moderately to slightly acidic (5.5–6.4) | 20.2% | 12.9% |
| Near neutral (6.5–7.3) | 41.6% | 41.8% |
| Alkaline (7.4 and up) | 20.2% | 33.6% |
| Not reported | 13.8% | 9.2% |
Texture
Show as a table
| Category | Gallatin County | Montana |
|---|---|---|
| Sandy | 0.0% | 0.8% |
| Loamy (loam, silt loam and similar) | 85.3% | 81.4% |
| Clayey (40%+ clay) | 0.2% | 7.3% |
| Organic (muck or peat) | 0.7% | 1.4% |
| Not reported (rock, urban land, etc.) | 13.8% | 9.2% |
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
- Gallatin County, Montana (FIPS 30031): 1,574,953 acres of mapped land, 14,444 acres of open water excluded. State comparisons pool all mapped land in Montana.
- 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.