Just a little geology background for the upcoming Titus Canyon run. Most of the geology in and around southern Nevada can be explained by four major events.
1) For a very long time, from 1,800 million years ago until 240 million years ago, what is now southern Nevada was a shallow sea; Utah and Arizona were the west coast of North America. The vast majority of the rocks around here were deposited on the seafloor then: limestones, shales, and other types. The rocks at the end of the run, on the western part of Titus Canyon, are ocean sediments from this time period. These include some of the oldest rocks with fossilized hard body parts, and such familiar names from southern Nevada as the Nopah and Bonanza King formations.
2) After this, the ocean floor to the west began to be subducted under the western edge of the continent, causing the land here to be uplifted; southern Nevada has been up out of the sea since this time. Some interesting rocks got made, but we won’t see then on the Titus Canyon run. One of the largest mountain ranges in the country 240 million years ago was the Ouachita Mountains in Oklahoma. A huge river, easily the equal of today’s Mississippi River, ran westward through the Texas Panhandle and central New Mexico before turning northward in NE Arizona to flow north through western Utah and out to sea in central Nevada. Our area was drained by tributaries that ran northward from other mountains to our south, into this river. Many hundreds of feet of sandstone, shale, and gravely conglomerate were deposited at this time on the floodplain. Exposure to oxygen rusted the iron in the soil, giving it a characteristic red color; this is the Chinle Formation of southern Nevada and Arizona. Next the area became a desert, the sand dunes of which are fossilized as the Aztec sandstone of Red Rock and the Navaho Sandstone of Zion. (Those two are really the same formation.) Farther west, Death Valley was still offshore at this time, and rocks were still being formed in the shallow seas, but none of them lie along the route of our Jeep run.
3) During the Cretaceous, from 145 to 65 million years ago, as the ocean floor to our west continued to be subducted under North America, the rocks of the ocean floor were young, warm, and buoyant, and didn’t want to sink. Instead of heading downward at a 45-degree angle as most bits of subducted ocean floor do, these stayed immediately under the rocks of North America, pushing up the rocks into mountains, and compressing them, causing some slabs of rock to slide up over others. (Geologists call this thrust-faulting.) Southern Nevada’s Spring Mountains were formed then, as were the southern Sierra Nevada. Death Valley was affected - the granite near Skidoo cooled underground at this time - but we won’t see rocks from this time along the run.
Along the middle of the run, from Red Pass north to Leadfield, we’ll have a mountain to our right made of rocks of the Titus Canyon Formation. At the time these were laid down roughly 35 million years ago, the area around the Grapevine Mountains (through which Titus Canyon is cut) was once again a flat floodplain, lush with vegetation and crossed by wandering rivers, much like Louisiana and Mississippi today. The area abounded in large grazing animals related to today’s horses and deer, and creatures that looked like rhinos (including the titanothere whose fossil skull gave Titanothere Canyon its name). Rodents scurried through the underbrush, and turtles and pupfish swam in the rivers.
4) As the subducted plate scraped eastward along the underside of North America, it stretched the plate above it, allowing widespread volcanism to spread eastward. The first part of our run, the eastern part, will cross a number of these young volcanic formations. A volcano on the Tonopah Test Range erupted 27 million years ago and buried the Grapevine Mountains area under a layer of hot ash 1,200 feet deep. We’ll drive past a ridge of 14-million-year old ash that was hot enough to weld itself together when it fell – a tuff. The first rocks we’ll reach after we climb the alluvial fan into the Grapevines are the basaltic lavas of a volcano 5 to 7 million years old, a volcano later split in half by the fault the lave followed to the surface, much like the Cleopatra/Hamblin volcano along Northshore Road at Lake Mead..
As the stretching of the crust continued, the landscape between Lake Mead and the Sierra Nevada was extended by over 150 miles from east to west. The extension proceeded at about an inch a year, causing north/south faults hundreds of miles long that cracked the land into N/S strips. Some of the strips tilted sideways, some sunk, other rose, the result was the many parallel N/S mountain ranges of the Basin and Range Province. By 2 to 3 million years ago, this extension reached Death Valley, the Grapevine Mountains rose, the floor of Death Valley sank, and the land took on its current shape. It’s hard for us today to appreciate how dramatic the landscape of Nevada really is, since the valleys are about half-filled with sediment washed off the mountains. Picture standing at Badwater today, looking west across Death Valley to the Panamint Range. The sediment that fills the valley is 11,000 feet deep – roughly as deep as from the valley floor to the top of the Panamints. Go get a giant DustBuster, clean all that out, and from the mountain tops to the valley floor would be about 22,000 feet!
See you all on the run!
(Edited to fix the typo in the second paragraph.)
_________________ A passenger and science geek: geology, meteorology, botany, astronomy, ...
Last edited by GeoPassenger David on Mon Nov 30, 2015 4:09 am, edited 1 time in total.
|