Soil series profile
Brocko soil series
Brocko is a well drained soil with a silt loam surface, mapped on 111,927 acres in 10 counties in MT. Hydrologic group B.
- Drainage class
- Well drained 98% of mapped acres
- Hydrologic group
- B 98% of mapped acres
- Typical topsoil pH
- 7.9 moderately alkaline · range 7.9–8.2
- Mapped area
- 112k acres in 10 counties, 1 state
Typical Brocko profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–4 in (A) | Silt loam | 7.9 | 14% | 14% | 2% |
| 4–12 in (Bk1) | Silt loam | 8.2 | 14% | 14% | 0.75% |
| 12–60 in (Bk2) | Silt loam | 8.2 | 14% | 14% | 0.25% |
What this means
What Brocko soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Brocko soils is moderately alkaline: pH 7.9 (most land between 7.9 and 8.2). 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 100% of mapped Brocko acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (>99% of mapped Brocko acres).
98% of mapped Brocko acres is moderately well to excessively drained, which suits most garden plants.
For lawns and yards
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 16% of the acres in mapped Brocko soils very limited, 84% somewhat limited and 0% not limited.
Only a licensed site evaluation or perc test at the actual lot decides whether a system is allowed and which design.
Where Brocko soil is found
Mapped acres
Brocko is mapped in Montana.
| County | Acres | Share of county land |
|---|---|---|
| Gallatin County, MT | 38,839 | 2.5% |
| Madison County, MT | 32,726 | 1.4% |
| Broadwater County, MT | 21,712 | 2.9% |
| Jefferson County, MT | 13,538 | 1.3% |
| Lewis and Clark County, MT | 4,836 | 0.2% |
| Beaverhead County, MT | 275 | 0.0% |
| Silver Bow County, MT | 2 | 0.0% |
| Meagher County, MT | 0 | 0.0% |
| Park County, MT | 0 | 0.0% |
| Sweet Grass County, MT | 0 | 0.0% |
Septic absorption fields
NRCS rating, share of Brocko acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 84.0% |
| Very limited | 16.0% |
Drainage, water table and flooding
Share of Brocko 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 2–25% (median 6%).
- 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 | 98.1% |
| Moderately well drained | 0.0% |
| Somewhat poorly drained | 1.9% |
| 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 | 98.0% |
| C: slow infiltration | 1.9% |
| D: very slow infiltration (clayey, shallow or wet) | 0.1% |
| 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 Brocko (component kind "Series") in SSURGO: 111,927 acres.
- Method
- Shares are by mapped acres of Brocko components. The profile comes from the single largest Brocko component. Full methodology.