Tuesday, February 28, 2017

Streams in the Desert: Red Rock Canyon State Park

On my recent geology field studies trip to Death Valley, we made a side trip to another beautiful and geologically rich place: Red Rock Canyon State Park.  Located on Highway 14 north of the town of Mojave, Red Rock Canyon State Park offers visitors opportunities for hiking, camping and more in a stunning desert landscape of red rock formations.  But due to the incessant rain, our time at Red Rock Canyon was relatively brief.

The impressive layered cliffs at Red Rock Canyon are part of the Ricardo Formation, an assemblage of rock layers that are unique and distinct enough to be separated from surrounding rock.  Looking closely at the layers, you will notice layers of red, brown and gray sandstone, pebbly conglomerate, very fine-textured gray clay, and both light-colored rhyolitic tuff and dark basalt from volcanic eruptions. 

Layers of sandstone and clay indicate that these deposits were laid down in the lakes, rivers and floodplains of a terrestrial landscape.  Conglomerates form as highly energetic water slows down and dumps its load of pebbles and cobbles; they are often indicative of alluvial fans.  In this case, rapid streams flowed from the Sierra Nevada mountains, as indicated by pieces of granite contained in the sediment.  The slight tilt of the layers was caused by more recent movement along the nearby Garlock fault.  Folds in the rock are the result of erosion by wind and water.

From these pieces of evidence, geologists are able to interpret the landscape and can piece together a picture of what this area was like millions of years ago.  5-20 million years ago, during the Miocene Epoch, the area that is now Red Rock Canyon State Park (and surrounding desert areas) was a relatively flat coastal plain, crossed by rivers making their way to the coast.  At that time, the coastline was just east of present-day Bakersfield, near Sharktooth Hill.  The Sierra Nevada had not risen to its present height, which meant there was no rain shadow effect and no desert; the area had a wet, humid and rather tropical climate dominated by a vast grass prairie. 

The prairie supported an array of grazing animals, the ancestors of modern species of horses, camels and deer, as well as their predators, such as an ancestral form of the saber-toothed cat and the amphicyon, a sort of bear-dog.  Red Rock Canyon State Park preserves the most complete Miocene-age (5-24 million years) vertebrate fossil record in North America.

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