“The result is a chain of ancient volcanic fields that started over 16 million years ago near the Idaho/Nevada/Oregon border and that gets progressively younger across southwestern Idaho and the eastern Snake River Plain.”
Geologists have identified seven volcanic fields in the northwest US, starting with the McDermitt field about 16.5 million years ago.
The volcanic field formed on the border between Oregon and Nevada just south of the Columbia River Basalt.
About 15 million years ago, the hotspot then fed the Owyhee-Humboldt field to the east of McDermitt.
The hotspot then continued northeast, forming the Bruneau-Jarbidge, Twin Falls and Heise fields.
source: express.co.uk