 Twenty million years ago, crustal extension associated with the Basin and Range Province caused extensive volcanism in the Sierra.About 10 Ma, the Sierra Nevada started to form when a block of crust between the Coast Range and the Basin and Range Province started to tilt to the west as heat from the Basin and Range extension thinned the eastern part of the block, making it more buoyant than the western portion of the block.Rivers started cutting deep canyons on both sides of the range.