Soil series profile
Hillon soil series
Hillon is a well drained soil with a clay loam surface, mapped on 1,242,898 acres in 17 counties in MT. Hydrologic group C.
- Drainage class
- Well drained 100% of mapped acres
- Hydrologic group
- C 100% of mapped acres
- Typical topsoil pH
- 7.9 moderately alkaline · range 7.8–8.0
- Mapped area
- 1.2M acres in 17 counties, 1 state
Typical Hillon profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–3 in (A) | Clay loam | 8.0 | 31% | 35% | 1.5% |
| 3–14 in (Bk1) | Clay loam | 8.2 | 32% | 35% | 1% |
| 14–29 in (Bk2) | Clay loam | 8.6 | 32% | 35% | 0.75% |
| 29–41 in (BCyz) | Clay loam | 8.0 | 33% | 34% | 0.5% |
| 41–79 in (Cz) | Clay loam | 7.8 | 33% | 34% | 0.5% |
What this means
What Hillon soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Hillon soils is moderately alkaline: pH 7.9 (most land between 7.8 and 8.0). 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 Hillon acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is loam (48% of mapped Hillon acres).
100% of mapped Hillon 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 Hillon 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 Hillon soil is found
Mapped acres
Hillon is mapped in Montana.
| County | Acres | Share of county land |
|---|---|---|
| Phillips County, MT | 238,422 | 6.4% |
| Hill County, MT | 185,825 | 10.1% |
| Chouteau County, MT | 162,395 | 6.5% |
| Blaine County, MT | 149,353 | 5.5% |
| Liberty County, MT | 128,030 | 14.1% |
| Toole County, MT | 124,984 | 11.6% |
| Valley County, MT | 119,866 | 3.7% |
| Pondera County, MT | 38,959 | 3.7% |
| Teton County, MT | 34,086 | 2.5% |
| McCone County, MT | 23,715 | 1.4% |
| Roosevelt County, MT | 18,737 | 1.2% |
| Cascade County, MT | 12,891 | 0.8% |
| Glacier County, MT | 4,528 | 0.3% |
| Dawson County, MT | 667 | 0.0% |
| Garfield County, MT | 321 | 0.0% |
| Daniels County, MT | 66 | 0.0% |
| Wibaux County, MT | 53 | 0.0% |
Septic absorption fields
NRCS rating, share of Hillon 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 Hillon 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 5–38% (median 10%).
- 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 | 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 | 100.0% |
| D: very slow infiltration (clayey, shallow or wet) | 0.0% |
| 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 Hillon (component kind "Series") in SSURGO: 1,242,898 acres.
- Method
- Shares are by mapped acres of Hillon components. The profile comes from the single largest Hillon component. Full methodology.