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.