Foothills and Valleys Ecoregion Key
| 1 | 1st order, origin from Valley Foor groundwater output | Spring Creek | |
| 1 | 1st-2nd order or <30 miles long | Headwaters Foothills River | |
| 1 | 3rd-4th order or >30 and <60 miles long | Go To 2 Below | |
| 1 | 4th-5th order, >60 miles long and a direct tributary to the Yellowstone or Missouri River | Intermountain Transitional River | |
| 2 | Cool-cold water tributaries that originate in the foothills and flow out to prairie rivers that are too warm to support coldwater fisheries | Small Transitional Foothills River | |
| 2 | Coldwater tributaries that flow to foothills and valley intermountain transitional rivers that maintain coldwater fisheries | Small Foothills River | |
