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Geology of the National Parks - Death Valley

 

click for timescale Death Valley National Park through time

The Earth Shook, The Sea Withdrew: Mesozoic time

During Late Paleozoic and Mesozoic time (225 - 65 million years ago), the Death Valley landscape changed dramatically. The quiet, sea-covered continental margin was replaced by erupting volcanoes, uplifting mountains, compressional thrusting. These changes were brought about by a tectonic collision to the west.

The western edge of the North American continent was pushed against the oceanic plate under the Pacific Ocean. A deep trench formed, and the Pacific oceanic plate began to sink (subduct) beneath the more buoyant continental rock of North America. A chain of volcanoes pushed through the continental crust parallel to the deep trench, fed by magma rising from the subducting oceanic plate as it entered Earth's hot interior. Thousands of feet of lavas erupted, pushing the ocean over 200 miles to the west. The Death Valley region was no longer coastal real estate, as it had been for the previous billion years.

Granite

The Skidoo townsite in 1906
Skidoo townsite in 1906.

Most of the volcanic activity was centered just to the west of Death Valley, although some of the oldest Mesozoic rocks are exposed in the southern Panamint Range. The deep magma chambers feeding the volcanoes eventually cooled and solidified, forming the granites widely exposed in the Sierra Nevada Mountains. A few of these granitic bodies intruded the Panamint and Cottonwood Mountains, but these rocks are not easily accessible. One of these relatively small granitic plutons emplaced 67-87 million years ago, right near the end of the Mesozoic Era, spawned one of the more profitable precious metal deposits in Death Valley, giving rise to the town and mines of Skidoo (although these gold deposits were quite small compared to the larger California goldfields west of the Sierra Nevada Mountains).

Death Valley itself was a broad, mountainous region during this time. Mountains are mostly sites of erosion, not deposition, and the sediments worn off the Death Valley region were shed both east and west carried by wind and water; the eastern sediments which ended up in Colorado are now famous for their dinosaur fossils.

Thrust-faults

During this continental collision and volcanism, Death Valley's older rocks were squeezed and cooked, adding another episode of metamorphism to their already complex history. Some thick layers of rock (miles thick!) were also shoved many miles eastward along thrust faults (reverse faults), and in some cases, older rocks were thrown up over younger rocks, just to confuse future geologists!

Move forward in time | | Quiet to chaos (Cenozoic time)
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