Soil series profile
Kobase soil series
Kobase is a well drained soil with a silty clay loam surface, mapped on 576,648 acres in 31 counties across 2 states. Hydrologic group C.
- Drainage class
- Well drained >99% of mapped acres
- Hydrologic group
- C 98% of mapped acres
- Typical topsoil pH
- 7.5 slightly alkaline · range 7.5–7.9
- Mapped area
- 577k acres in 31 counties, 2 states
Typical Kobase profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–6 in (Ap) | Silty clay loam | 7.5 | 34% | 19% | 1.5% |
| 6–15 in (Bw) | Silty clay loam | 7.9 | 39% | 18% | 0.75% |
| 15–31 in (Bk) | Silty clay loam | 7.9 | 39% | 18% | 0.75% |
| 31–60 in (Bky) | Silty clay loam | 8.5 | 39% | 18% | 0.75% |
What this means
What Kobase soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Kobase soils is slightly alkaline: pH 7.5 (most land between 7.5 and 7.9). 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 >99% of mapped Kobase acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silty clay loam (94% of mapped Kobase acres).
100% of mapped Kobase 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 100% of the acres in mapped Kobase soils very limited, 0% somewhat limited and 0% not 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.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Kobase soil is found
Mapped acres
Kobase is mapped in Montana and Colorado.
| County | Acres | Share of county land |
|---|---|---|
| Garfield County, MT | 112,448 | 3.9% |
| Custer County, MT | 73,049 | 2.9% |
| Rosebud County, MT | 47,805 | 1.0% |
| Chouteau County, MT | 46,637 | 1.9% |
| Liberty County, MT | 38,826 | 4.3% |
| Golden Valley County, MT | 27,876 | 3.8% |
| Pondera County, MT | 23,563 | 2.2% |
| Carter County, MT | 22,035 | 1.2% |
| Prairie County, MT | 21,137 | 1.9% |
| Musselshell County, MT | 20,007 | 1.7% |
| Phillips County, MT | 17,865 | 0.5% |
| Teton County, MT | 17,434 | 1.3% |
| Toole County, MT | 16,349 | 1.5% |
| Rio Blanco County, CO | 16,286 | 0.8% |
| Dawson County, MT | 11,768 | 0.8% |
| Big Horn County, MT | 10,677 | 0.2% |
| Wheatland County, MT | 9,772 | 1.2% |
| Fergus County, MT | 9,262 | 0.3% |
| Sweet Grass County, MT | 8,027 | 0.6% |
| Hill County, MT | 7,441 | 0.4% |
| Fallon County, MT | 5,523 | 0.5% |
| Petroleum County, MT | 5,239 | 0.5% |
| Richland County, MT | 4,756 | 0.3% |
| McCone County, MT | 1,424 | 0.1% |
| Lewis and Clark County, MT | 610 | 0.0% |
| Stillwater County, MT | 299 | 0.0% |
| Blaine County, MT | 131 | 0.0% |
| Wibaux County, MT | 83 | 0.0% |
| Park County, MT | 37 | 0.0% |
| Meagher County, MT | 17 | 0.0% |
| Yellowstone County, MT | 3 | 0.0% |
Septic absorption fields
NRCS rating, share of Kobase acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 0.0% |
| Very limited | 100.0% |
Drainage, water table and flooding
Share of Kobase acres
- Depth to seasonal high water table
- About 3.9 feet (47 in) (median where reported).
- Flooding
- Not mapped as flooding on most acres.
- Slope
- Typically 2–9% (median 5%).
- Topsoil organic matter
- Median 1.5%.
Drainage class
Show as a table
| Category | Share of acres |
|---|---|
| Excessively drained | 0.0% |
| Somewhat excessively drained | 0.0% |
| Well drained | 99.8% |
| Moderately well drained | 0.2% |
| 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 | 98.2% |
| D: very slow infiltration (clayey, shallow or wet) | 1.8% |
| 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 Kobase (component kind "Series") in SSURGO: 576,648 acres.
- Method
- Shares are by mapped acres of Kobase components. The profile comes from the single largest Kobase component. Full methodology.