Strongly bimodal, basalt-rhyolite volcanism of the High Lava Plains Province of Oregon followed the Middle Miocene flood basalts of the Pacific Northwest and extends to recent time. During the 8 m.y. of volcanism recorded in the central High Lava Plains, in western Harney Basin, three distinct mafic magmatic trends originate...
The Rattlesnake Ash-Flow Tuff erupted 7.05±0.01 Ma from the western Harney Basin, southeastern Oregon. The location of the vent area is inferred based on vent-ward increases in size of pumices, in degree of welding, and in degree of post-emplacement crystallization. Today's outcrops cover 9000 km2 and estimated original outcrop coverage...