Basin and range topography

Basin and range topography is a landscape of alternating, roughly parallel mountain ranges and valleys. It results from crustal extension, driven by mantle upwelling, gravitational collapse, crustal thickening or the relaxation of confining stresses, which thins and fractures the upper crust into a series of long parallel normal faults. The blocks of rock between the faults then subside, rise or tilt, producing the alternating basins and ranges. Where faults dip in opposite directions the result is symmetrical horsts and grabens, with equal slopes on both sides, while tilted block faulting along a detachment fault gives ranges with one steep side and one gentle side. Thinning crust also lets mantle heat melt rock more easily, which can raise volcanic activity. The best-known example is the Basin and Range Province of the southwestern United States and northwestern Mexico, where extension began in the early Miocene, about 17 million years ago, and the Aegean Sea Plate is another.