The Basin and Range is the result of the North American plate being stretched as the smaller plates to its west were subducted and broken up during the Miocene Epoch (23 to 5 million years ago). The hot lower crust stretched in a plastic fashion while the brittle upper crust tore into rocky strips that foundered in the soft rock below, tilting into widely spaced ranges with basins between. This activity was accompanied by ferocious volcanism and the emplacement of widespread metal deposits. During wet times the basins became lakes; in dry times like today most basins dried into dusty playas. Most of these events are visible in the rocks and landforms along the Outback Scenic Byway.