| Age | Formation | Member | Age (ma) |
|---|---|---|---|
Miocene |
Saddle Mountains Basalt | Lower Monumental Member | 6 |
| Ice Harbor Member | 8.5 | ||
| Buford Member | |||
| Elephant Mountain Member | 10.5 | ||
| Pomona Member | 12 | ||
| Esquatzel Member | |||
| Weissenfels Ridge Member | |||
| Asotin Member | 13 | ||
| Wilbur Creek Member | |||
| Umatilla Member | 13.5 | ||
| Wanapum Basalt | Priest Rapids Member | 15 | |
| Basalt of Rosalia | |||
| Roza Member | |||
| Frenchman Springs Member | 15.3 | ||
| Eckler Mountain Member | |||
| Prineville Basalt | |||
| Grande Ronde Basalt | 15.6 | ||
| Picture Gorge Basalt | 16.4 | ||
| Imnaha Basalt | 16.7 | ||
| Steens Basalt | 16.8 |