New dating methods show that the sand system developed in five main pulses over the last 25,000 years, partly over-lapping in time with lake highstands and the youngest volcanism in the region. Some of the more striking rock formations in the Mojave National Preserve lie in the Granite Mountains. These granitic rocks have eroded into unusual rounded shapes that include spires, perched boulders, and curved cliff faces. The rocks are composed of interlocking mineral grains, which disaggregate into individual grains as the rock surface weathers. This characteristic, along with the massive, non-layered nature of granitoids and the lack of closely spaced fractures in these outcrops, resulted in the curved weathering surfaces in the mountains.
Granitic rocks represent the roots of ancient continental-margin volcanic systems.
The Mojave National Preserve lies within a belt of late Mesozoic granites that parallels the western continental margin from Mexico to Canada. The granites formed at depth within a volcanically active mountain range comparable in geologic setting to the Andes Mountains chain in South America. The granitoids formed by the slow cooling and solidification of molten magma bodies that developed above sinking slabs of oceanic crust overridden by the edge of the continent. At least 55 or 60 million years elapsed between the crystallization of the last Mesozoic magma bodies and deposition of the youngest-preserved overlying strata. The Mojave National Preserve probably formed a highlands during much of this period and erosion gradually stripped off Paleozoic and Mesozoic sedimentary rocks overlying the granites.