Rhyolite rocks are generally older and covered by younger basalt. Most of the surface of the ESRP is composed of low-profile basaltic shield volcanoes that coalesce into a low-relief plain.

Previously, it was thought that the youngest eruption in the region was the rhyolite lava of the Pitchstone Plateau about 70,000 years ago, while the youngest known basalt flow was 120,000 years old. ...

Yellow represents basalt, red rhyolite, and orange basalt-to-rhyolite transition zones. The purple triangles are the magnetotelluric monitoring stations. Picture: Bennington et al., Nature, 2025.

The High Lava Plains - a ~10 million year old chain of rhyolite and basalt volcanism that gets younger to the west -- intersect the Cascade Range near Bend, Oregon. The Basin & Range -- the province ...