Soil Strata
USGS-derived soil composition + dig-difficulty score per sub-region · 27 regions across the six target states
| Region | State | Primary strata | Composition | Notes | |
|---|---|---|---|---|---|
| Grand Mesa | CO | Karst limestone | Rock 32% · Clay 34% · Silt 34% | 9/10 | Voids and rock; assume hammer and contingency. |
| Blue Ridge Foothills | NC | Karst limestone | Rock 27% · Clay 47% · Gravel 26% | 9/10 | Voids and rock; assume hammer and contingency. |
| Laramie Basin | WY | Glacial till with cobble | Loam 20% · Silt 19% · Clay 61% | 8/10 | Cobble deflects the head; expect re-bores. |
| Powder River | WY | Glacial till with cobble | Loam 42% · Clay 34% · Cobble 24% | 8/10 | Cobble deflects the head; expect re-bores. |
| Green River Valley | WY | Glacial till with cobble | Sand 30% · Clay 24% · Cobble 46% | 8/10 | Cobble deflects the head; expect re-bores. |
| Uinta Basin | UT | Glacial till with cobble | Rock 41% · Loam 41% · Sand 18% | 8/10 | Cobble deflects the head; expect re-bores. |
| Wind River Corridor | WY | Decomposed granite | Silt 33% · Gravel 38% · Loam 29% | 7/10 | Rock saw or hammer on most of the route. |
| Cache Valley | UT | Decomposed granite | Sand 32% · Clay 34% · Cobble 34% | 7/10 | Rock saw or hammer on most of the route. |
| Iron County | UT | Shale and siltstone | Rock 36% · Cobble 26% · Loam 38% | 6/10 | Rippable, but bit wear runs high. |
| Panhandle East | FL | Shale and siltstone | Silt 31% · Sand 37% · Cobble 32% | 6/10 | Rippable, but bit wear runs high. |
| Nature Coast | FL | Shale and siltstone | Loam 22% · Silt 33% · Gravel 45% | 6/10 | Rippable, but bit wear runs high. |
| Big Bend | FL | Shale and siltstone | Loam 29% · Cobble 33% · Sand 38% | 6/10 | Rippable, but bit wear runs high. |
| Mississippi Bluffs | TN | Shale and siltstone | Sand 26% · Gravel 34% · Clay 40% | 6/10 | Rippable, but bit wear runs high. |
| San Luis Basin | CO | Red clay over saprolite | Silt 50% · Loam 24% · Rock 26% | 5/10 | Saprolite slows bores below six feet. |
| Treasure Coast | FL | Red clay over saprolite | Silt 27% · Sand 30% · Rock 43% | 5/10 | Saprolite slows bores below six feet. |
| Cumberland Plateau | TN | Red clay over saprolite | Cobble 21% · Loam 29% · Sand 50% | 5/10 | Saprolite slows bores below six feet. |
| Tennessee Valley | TN | Red clay over saprolite | Loam 29% · Cobble 36% · Silt 35% | 5/10 | Saprolite slows bores below six feet. |
| Arkansas Valley | CO | Coastal sand with high water | Cobble 16% · Rock 41% · Loam 43% | 4/10 | Shallow water table; dewatering on deeper vaults. |
| Wasatch Front | UT | Coastal sand with high water | Cobble 49% · Clay 17% · Sand 34% | 4/10 | Shallow water table; dewatering on deeper vaults. |
| Front Range North | CO | Silty clay loam | Rock 35% · Gravel 26% · Silt 39% | 3/10 | Straightforward plowing; bore only at crossings. |
| Pikes Peak Corridor | CO | Sandy loam over caliche | Sand 46% · Cobble 39% · Rock 15% | 3/10 | Straightforward plowing; bore only at crossings. |
| Highland Rim | TN | Sandy loam over caliche | Silt 35% · Loam 15% · Cobble 50% | 3/10 | Straightforward plowing; bore only at crossings. |
| Sandhills | NC | Silty clay loam | Sand 37% · Clay 24% · Cobble 39% | 3/10 | Straightforward plowing; bore only at crossings. |
| Coastal Plain | NC | Sandy loam over caliche | Loam 36% · Rock 32% · Sand 32% | 3/10 | Straightforward plowing; bore only at crossings. |
| Pee Dee | NC | Sandy loam over caliche | Clay 44% · Silt 37% · Rock 19% | 3/10 | Straightforward plowing; bore only at crossings. |
| Central Ridge | FL | Alluvial sand | Gravel 27% · Silt 38% · Sand 35% | 2/10 | Easy trenching, watch for cave-in in dry sand. |
| Piedmont Triad | NC | Alluvial sand | Loam 41% · Cobble 40% · Silt 19% | 2/10 | Easy trenching, watch for cave-in in dry sand. |