Geologic history of the western United States in a cliff face in Death Valley National Park
Of the many geologic events that shaped the western United States since the beginning of the Paleozoic Era, five really stand out. In approximate chronological order, these events include the accumulation of tens of thousands of feet of sedimentary rock on a passive margin, periods of compressional mountain building that folded and faulted those rocks during much of the Mesozoic–likely driven by the accretion of terranes, intrusion of subduction-related granitic rock (such as the Sierra Nevada) during the Jurassic and Cretaceous, volcanic activity during the late Cenozoic, and mountain-building by crustal extension during the late Cenozoic and continuing today. This photo on the western edge of Panamint Valley in Death Valley National Park of California, captures all five.
The photograph below shows an interpretation. Paleozoic rock is folded because of the Late Paleozoic-early Mesozoic compressional mountain-building; it’s intruded by Jurassic age granitic rock, an early phase of Sierran magmatism that took place just to the west; the granitic rock is overlain by Late Cenozoic basalt flows, and everything is cut by a normal (extensional) fault. And there is also a dike that cuts the Paleozoic rock –probably a feeder for the basalt flows.
So this is all nerdy geology cross-cutting relations talk –but here’s the point: in this one place, you can see evidence for 100s of millions of years of Earth History. Earth is old old old! THAT’S why I love geology!
And for those of you who crave geologic contacts? This photo has all three: depositional, between the basalt and underlying rock; intrusive, between the Mesozoic granite and the folded Paleozoic rock; fault, the steeply dipping black line between the basalt and the Paleozoic rock. Another reason why I love geology!
click here to see photos and explanations of geologic contacts.
or click here for a slideshow of Death Valley geology.