<P> Evidence suggests that the less - recognized southern portion of the province is bounded on the east by the Laramide Thrust Front of the Sierra Madre Oriental and on the west by the Gulf of California and Baja Peninsula with notably less faulting apparent in the Sierra Madre Occidental in the center of the southernmost Basin and Range Province . </P> <P> Common geographic features include numerous endorheic basins, ephemeral lakes, plateaus, and valleys alternating with mountains (as described below). The area is mostly arid and sparsely populated, although there are several major metropolitan areas, including Mexico City, the largest city in the western hemisphere . </P> <P> It is generally accepted that basin and range topography is the result of extension and thinning of the lithosphere, which is composed of crust and upper mantle . Extensional environments like the Basin and Range are characterized by listric normal faulting, or faults that level out with depth . Opposing normal faults link at depth producing a horst and graben geometry, where horst refers to the upthrown fault block and graben to the down dropped fault block . </P> <P> The average crustal thickness of the Basin and Range Province is approximately 30--35 km and is comparable to extended continental crust around the world . The crust in conjunction with the upper mantle comprises the lithosphere . The base of the lithosphere beneath the Basin and Range is estimated to be about 60--70 km . Opinions vary regarding the total extension of the region; however, the median estimate is about 100% total lateral extension . Total lateral displacement in the Basin and Range varies from 60--300 km since the onset of extension in the Early Miocene with the southern portion of the province representing a greater degree of displacement than the north . Evidence exists to suggest that extension initially began in the southern Basin and Range and propagated north over time . </P>

What type of mountain is the basin and range