Soil series profile
Lonna soil series
Lonna is a well drained soil with a silt loam surface, mapped on 1,322,003 acres in 30 counties across 3 states. Hydrologic group B.
- Drainage class
- Well drained 100% of mapped acres
- Hydrologic group
- B 50% of mapped acres
- Typical topsoil pH
- 7.9 moderately alkaline · range 7.6–7.9
- Mapped area
- 1.3M acres in 30 counties, 3 states
Typical Lonna profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–5 in (A) | Silt loam | 7.9 | 24% | 23% | 2% |
| 5–10 in (Bw) | Silt loam | 8.2 | 26% | 24% | 0.75% |
| 10–30 in (Bk) | Silt loam | 8.5 | 27% | 23% | 0.25% |
| 30–60 in (BC) | Silt loam | 8.5 | 23% | 26% | 0.25% |
What this means
What Lonna soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Lonna soils is moderately alkaline: pH 7.9 (most land between 7.6 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 100% of mapped Lonna acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is silt loam (93% of mapped Lonna acres).
100% of mapped Lonna 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 58% of the acres in mapped Lonna soils very limited, 42% 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 Lonna soil is found
Mapped acres
Lonna is mapped in Montana, North Dakota and Wyoming.
| County | Acres | Share of county land |
|---|---|---|
| Garfield County, MT | 220,647 | 7.6% |
| Prairie County, MT | 211,161 | 19.0% |
| Dawson County, MT | 193,491 | 12.8% |
| Rosebud County, MT | 137,564 | 2.8% |
| Custer County, MT | 114,225 | 4.6% |
| Big Horn County, MT | 70,972 | 1.6% |
| Richland County, MT | 66,592 | 4.9% |
| Golden Valley County, ND | 54,475 | 8.5% |
| Billings County, ND | 45,634 | 6.2% |
| Fallon County, MT | 42,580 | 4.1% |
| McKenzie County, ND | 19,887 | 1.1% |
| Slope County, ND | 17,799 | 2.3% |
| Stillwater County, MT | 16,877 | 1.5% |
| Chouteau County, MT | 15,953 | 0.6% |
| McCone County, MT | 15,123 | 0.9% |
| Valley County, MT | 13,414 | 0.4% |
| Toole County, MT | 10,773 | 1.0% |
| Dunn County, ND | 10,347 | 0.8% |
| Wibaux County, MT | 8,967 | 1.6% |
| Sweetwater County, WY | 8,471 | 0.1% |
| Liberty County, MT | 7,544 | 0.8% |
| Yellowstone County, MT | 5,994 | 0.4% |
| Pondera County, MT | 5,279 | 0.5% |
| Hill County, MT | 3,072 | 0.2% |
| Carter County, MT | 2,592 | 0.1% |
| Bowman County, ND | 1,458 | 0.2% |
| Wheatland County, MT | 727 | 0.1% |
| Teton County, MT | 186 | 0.0% |
| Sweet Grass County, MT | 180 | 0.0% |
| Golden Valley County, MT | 20 | 0.0% |
Septic absorption fields
NRCS rating, share of Lonna acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 41.8% |
| Very limited | 58.2% |
Drainage, water table and flooding
Share of Lonna 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 2–14% (median 5%).
- 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 | 50.2% |
| C: slow infiltration | 49.2% |
| D: very slow infiltration (clayey, shallow or wet) | 0.6% |
| 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 Lonna (component kind "Series") in SSURGO: 1,322,003 acres.
- Method
- Shares are by mapped acres of Lonna components. The profile comes from the single largest Lonna component. Full methodology.