Soil series profile
Riddles soil series
Riddles is a well drained soil with a sandy loam surface, mapped on 490,846 acres in 39 counties across 4 states. Hydrologic group B.
- Drainage class
- Well drained 100% of mapped acres
- Hydrologic group
- B 96% of mapped acres
- Typical topsoil pH
- 6.5 slightly acidic · range 6.2–6.5
- Mapped area
- 491k acres in 39 counties, 4 states
Typical Riddles profile
Texture and pH by depth
Show as a table
| Depth | Texture | pH | Clay | Sand | Organic matter |
|---|---|---|---|---|---|
| 0–8 in (Ap) | Sandy loam | 6.2 | 5% | 55% | 1.9% |
| 8–13 in (E) | Sandy loam | 5.3 | 6% | 53% | 0.5% |
| 13–23 in (Bt1) | Sandy clay loam | 6.3 | 23% | 51% | 0.3% |
| 23–42 in (Bt2) | Sandy clay loam | 5.7 | 30% | 52% | 0.2% |
| 42–55 in (BC) | Sandy loam | 6.1 | 19% | 55% | 0.2% |
| 55–79 in (C) | Sandy loam | 8.2 | 9% | 68% | 0.2% |
What this means
What Riddles soil means for gardens, lawns and septic systems
For gardens
Typical topsoil in Riddles soils is slightly acidic: pH 6.5 (most land between 6.2 and 6.5), the range most vegetables, flowers and lawn grasses prefer.
Loamy topsoil (loam, silt loam and similar) covers 100% of mapped Riddles acres: generally the easiest soil to garden, holding moisture without staying waterlogged. The most common surface texture is sandy loam (45% of mapped Riddles acres).
100% of mapped Riddles 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 12% of the acres in mapped Riddles soils very limited, 89% 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 Riddles soil is found
Mapped acres
Riddles is mapped in Michigan, Indiana, Ohio and Illinois.
| County | Acres | Share of county land |
|---|---|---|
| Jackson County, MI | 77,470 | 17.2% |
| Hillsdale County, MI | 36,028 | 9.4% |
| Oakland County, MI | 34,877 | 6.3% |
| Marshall County, IN | 33,957 | 12.0% |
| Berrien County, MI | 31,330 | 8.6% |
| Wayne County, OH | 29,501 | 8.3% |
| Kosciusko County, IN | 25,034 | 7.3% |
| Cass County, IN | 24,229 | 9.2% |
| LaPorte County, IN | 20,820 | 5.4% |
| Kalamazoo County, MI | 18,077 | 5.0% |
| Van Buren County, MI | 17,712 | 4.6% |
| Porter County, IN | 17,291 | 6.5% |
| Noble County, IN | 17,070 | 6.5% |
| Elkhart County, IN | 16,522 | 5.6% |
| Steuben County, IN | 14,912 | 7.6% |
| Fulton County, IN | 13,660 | 5.8% |
| Branch County, MI | 10,441 | 3.2% |
| St. Joseph County, IN | 8,701 | 3.0% |
| Calhoun County, MI | 8,080 | 1.8% |
| Cass County, MI | 6,751 | 2.1% |
| Wabash County, IN | 6,071 | 2.3% |
| St. Joseph County, MI | 5,434 | 1.7% |
| Ingham County, MI | 4,142 | 1.2% |
| Allegan County, MI | 3,799 | 0.7% |
| White County, IN | 2,049 | 0.6% |
| Pulaski County, IN | 2,049 | 0.7% |
| Carroll County, IN | 1,683 | 0.7% |
| Washtenaw County, MI | 1,346 | 0.3% |
| Whitley County, IN | 815 | 0.4% |
| Ashland County, OH | 274 | 0.1% |
| Macomb County, MI | 224 | 0.1% |
| Stark County, OH | 133 | 0.0% |
| Summit County, OH | 110 | 0.0% |
| Medina County, OH | 109 | 0.0% |
| Lapeer County, MI | 68 | 0.0% |
| Iroquois County, IL | 43 | 0.0% |
| LaGrange County, IN | 27 | 0.0% |
| Allen County, IN | 5 | 0.0% |
| Genesee County, MI | 1 | 0.0% |
Septic absorption fields
NRCS rating, share of Riddles acres
Show as a table
| Category | Share of acres |
|---|---|
| Not limited | 0.0% |
| Somewhat limited | 88.5% |
| Very limited | 11.5% |
Drainage, water table and flooding
Share of Riddles 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 3–10% (median 4%).
- Topsoil organic matter
- Median 1.9%.
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 | 96.1% |
| C: slow infiltration | 3.9% |
| 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 Riddles (component kind "Series") in SSURGO: 490,846 acres.
- Method
- Shares are by mapped acres of Riddles components. The profile comes from the single largest Riddles component. Full methodology.