Review of the Geologic Evolution of Southern Nevada
The oldest rock in the region is 1.7 billion-year-old basement complex - black schists and pink granites of the Vishnu Group - representing the ancient core of the continent. Behind you lying on top of the basement complex and exposed in the western face of Frenchman Mountain are Paleozoic sedimentary rocks deposited by the shallow sea that repeatedly advanced and retreated across the very flat western margin of North American during the Paleozoic Era. The fossilized remains of ancient sea animals are abundant in these rocks.
The Paleozoic Era - when Nevada was covered by the sea
During the Mesozoic Era thick slabs of Paleozoic rock were shoved eastward during a major mountain building episode - the Sevier Orogeny - that involved horizontal compression of the Earth's crust. The Spring Mountains consist primarily of massive slabs of Paleozoic carbonate rocks that were stacked one upon the other as a result of this compression. The major mountain-building episodes that affected Southern Nevada - Mesozoic compression and Cenozoic extension - were caused by interactions between the huge plates of the Earth's crust.
The Mesozoic Era - squeezing from the west
The Las Vegas Valley and the major topographic features of Southern Nevada were created during a recent episode of crustal deformation in the Cenozoic Era. This was the same episode of crustal extension - or 'pulling apart' of the Earth's crust - that caused Frenchman Mountain to move about 50 miles to the west. This 'pulling apart' occurred during the Miocene Epoch (23 to 6 million years ago), which is a subdivision of the Cenozoic Era.
The Cenozoic Era - basin and range topography develops