The Nevadaplano was a high plateau that is proposed to have covered parts of southwestern North America during the late Mesozoic and early Cenozoic, located in the present-day US states of Idaho, Nevada, Utah and possibly others. It most likely formed during the Cretaceous as a consequence of subduction dynamics and may have reached elevations of 3 kilometres (9,800 ft) and more, although its elevation is controversial. It was flanked on the west by the Sierra Nevada, which was traversed by various valleys that came down from the Nevadaplano. Closed basins and numerous volcanic calderas covered the relatively flat Nevadaplano; large volcanic eruptions distributed ignimbrites over the plateau and down the valleys draining it.
During the Miocene, changes in the tectonic regime may have caused a collapse and dismemberment of the Nevadaplano. Tectonic extension gave rise to the Basin and Range province and separated the Sierra Nevada-Great Valley block from the Nevadaplano, forming today's landscape.