was a volcanic plain. Extension creates the Basin and Range Starting around 16 Ma in Miocene time and continuing into the present, a large part of the North American Plate in the region has been under extension by literally being pulled apart. Debate still surrounds the cause of this crustal stretching, but an increasingly popular idea among geologists called the slab gap hypothesis states that the spreading zone of the subducted Farallon Plate is pushing the continent apart. Whatever the cause, the result has been the creation of a large and still-growing region of relatively thin crust; the region grew an average of per year initially and then slowed to per year in the last 5 million years. Geologists call this region the Basin and Range Province. Extensional forces causes rock at depth to stretch like silly putty and rock closer to the surface to break along normal faults into downfallen basins called grabens; small mountain ranges known as horsts run parallel to each other on either side of the graben. Normally the number of horsts and grabens is limited, but in the Basin and Range region there are dozens of horst/graben structures, each roughly north–south trending. A succession of these extend from immediately east of the Sierra Nevada, through almost all of Nevada, and into western Utah and southern Idaho. The crust in the Death Valley region between Lake Mead and the southern Sierra Nevada has been extended by as much as . The Furnace Creek Fault system, located in what is now the northern part of Death Valley, started to move about 14 Ma and the Southern Death Valley Fault system likely began to move by 12 million years ago. Both fault systems move with a right-lateral, or dextral, offset along strike-slip faults. With such faults, the opposite side of the fault appears to be moving right when facing the fault from either side. Both fault systems run parallel to and at the base of the ranges. Very often the same faults move laterally and vertically, simultaneously making them strike-slip and normal (i.e. oblique-slip). These two systems are also offset from each other; the area between the offset is thus put under enormous oblique tension, which intensifies subsidence there; Furnace Creek Basin opened in this area and the rest of Death Valley followed in stages. One of the last stages was the formation of Badwater Basin, which occurred