“The termination Farallon Plate subduction probably made the Basin and Range.
As North America closed like a sliding trapdoor over the Farallon plate, the plate did not go quietly into the mantle night. It raged and raged, first searing vast tracts of the West with fiery volcanic clouds and then stretching the crust to make the Basin and Range. The plate’s death throes began about 43 million years ago, as it started to peel away fromthe base of the North American Plate to end the flat subduction episode that hoisted the Foreland Ranges. Restoring itself to normal subduction mode, the Farallon Plate began once again to crank out magma. The result was a maelstrom of volcanism that would rival even that of the later calderas of the Snake River Plain-to-Yellowstone tract. Between 43 and 21 million years ago, calderas opened fire all across what would become the Basin and Range. Incandescent clouds of volcanic ash incinerated the landscape—and every living thing on it—time and again before settling, crackling hot, to weld into layers of volcanic tuff. You can see these tuff layers today stacked up hundreds of feet thick throughout the ranges of the Basin and Range, painting the mountainsides with lovely bands of pink, ochre, and gold.”