Soil series profile
Gerdrum soil series
Gerdrum is a well drained soil with a loam surface, mapped on 736,490 acres in 33 counties across 3 states. Hydrologic group D.
- Drainage class
- Well drained 100% of mapped acres
- Hydrologic group
- D 100% of mapped acres
- Typical topsoil pH
- 7.2 neutral · range 7.2–7.2
- Mapped area
- 736k acres in 33 counties, 3 states
Typical Gerdrum profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–4 in (H1) | Loam | 7.2 | 24% | 39% | 2% |
| 4–15 in (H2) | Clay loam | 8.2 | 39% | 30% | 0.75% |
| 15–60 in (H3) | Clay loam | 8.5 | 38% | 31% | 0.25% |
What this means
What Gerdrum soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Gerdrum soils is neutral: pH 7.2, the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 94% of mapped Gerdrum acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is clay loam (68% of mapped Gerdrum acres).
100% of mapped Gerdrum acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
On 100% of mapped acres, rain soaks in slowly (hydrologic groups C and D, including dual groups that are D until drained). Expect runoff and puddles after heavy rain: core-aerate compacted lawns and keep ground sloping away from foundations.
For a septic system
For conventional septic absorption fields, NRCS rates 44% of the acres in mapped Gerdrum soils very limited, 1% somewhat limited and 55% not limited.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Gerdrum soil is found
Mapped acres
Gerdrum is mapped in Montana, South Dakota and Wyoming.
| County | Acres | Share of county land |
|---|---|---|
| Carter County, MT | 131,444 | 6.9% |
| Rosebud County, MT | 79,769 | 1.6% |
| Petroleum County, MT | 70,873 | 6.7% |
| Meade County, SD | 64,832 | 2.9% |
| Fergus County, MT | 57,966 | 2.1% |
| McCone County, MT | 39,223 | 2.3% |
| Fallon County, MT | 38,848 | 3.8% |
| Garfield County, MT | 33,953 | 1.2% |
| Phillips County, MT | 32,996 | 0.9% |
| Custer County, MT | 32,992 | 1.3% |
| Big Horn County, MT | 22,724 | 0.5% |
| Musselshell County, MT | 21,049 | 1.8% |
| Harding County, SD | 19,950 | 1.2% |
| Toole County, MT | 18,087 | 1.7% |
| Blaine County, MT | 12,205 | 0.4% |
| Prairie County, MT | 10,811 | 1.0% |
| Chouteau County, MT | 9,450 | 0.4% |
| Golden Valley County, MT | 7,964 | 1.1% |
| Hill County, MT | 7,385 | 0.4% |
| Wheatland County, MT | 4,642 | 0.6% |
| Teton County, MT | 4,355 | 0.3% |
| Lewis and Clark County, MT | 3,848 | 0.2% |
| Liberty County, MT | 3,793 | 0.4% |
| Carbon County, WY | 3,690 | 0.1% |
| Sweet Grass County, MT | 1,392 | 0.1% |
| Lincoln County, WY | 544 | 0.0% |
| Meagher County, MT | 490 | 0.0% |
| Stillwater County, MT | 420 | 0.0% |
| Pondera County, MT | 348 | 0.0% |
| Cascade County, MT | 270 | 0.0% |
| Valley County, MT | 99 | 0.0% |
| Glacier County, MT | 72 | 0.0% |
| Park County, MT | 8 | 0.0% |
Septic absorption fields
NRCS rating, share of Gerdrum acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 55.0% |
| Somewhat limited | 1.1% |
| Very limited | 43.8% |
Drainage, water table and flooding
Share of Gerdrum acres
- Depth to seasonal high water table
- None reported within about 6.5 feet (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 1–5% (median 4%).
- Topsoil organic matter
- Median 2%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 100.0% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 0.0% |
| Poorly drained | 0.0% |
| Very poorly drained | 0.0% |
Hydrologic soil group
Show as a table
| Category | Share of acres |
|---|---|
| A: fast infiltration (mostly sandy or gravelly) | 0.0% |
| B: moderate infiltration | 0.0% |
| C: slow infiltration | 0.0% |
| D: very slow infiltration (clayey, shallow or wet) | 100.0% |
| A/D: D as is, A if drained | 0.0% |
| B/D: D as is, B if drained | 0.0% |
| C/D: D as is, C if drained | 0.0% |
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
- All map unit components named Gerdrum (component kind "Series") in SSURGO: 736,490 acres.
- Method
- Shares are by mapped acres of Gerdrum components. The profile comes from the single largest Gerdrum component. Full methodology.