Originally Posted by LeeshaJoy
Uh, I live on the Idaho/Washington border, and about 99% of the rock in this area was laid down by the Yellowstone supervolcano.
Sort of. Major tangent ahead.
The most common rocks in eastern Washington into Idaho are the Columbia River Basalt Group
, which were a catastrophic series of huge effusive (i.e. runny Hawaii-style) eruptions. There is most likely some
relationship between the CRBG and the Yellowstone supervolcano-- the CRBG eruptions were about 17 million years ago in southeast Oregon/western Idaho, which just so happens to also be were and when the first of the explosive Yellowstone eruptions was. The super-thick basalt beds that cover your area are all millions of years old and aren't the result of the periodic explosive eruptions that will spell doom for everyone east of Yellowstone.