Stories tagged tectonics

Mar
29
2008

Red Rock Canyon: The gray Paleozoic limestones of the Spring Mountains loom over the younger Mesozoic sandstones.
Red Rock Canyon: The gray Paleozoic limestones of the Spring Mountains loom over the younger Mesozoic sandstones.Courtesy Mark Ryan
Even when I’m on vacation my attention is often drawn to things of science. Last week after a couple rigorous days in Las Vegas observing the various aspects of the Law of Attraction (“please make the next card an eight”) and my personal experiments in slot-machine probability and statistics, my wife and I took a break from all the razzle-dazzle to investigate a geological feature situated in the Spring Mountains about 20 miles west of the city.

Another view of Red Rock Canyon: The sandstones dwarf visitors in the distance.
Another view of Red Rock Canyon: The sandstones dwarf visitors in the distance.Courtesy Mark Ryan
Red Rock Canyon National Conservation Area covers 197,000 acres within the Mojave Desert and the namesake formation stands out colorfully against the stark grayness of the basin and range topography for which Nevada is so well known. The park offers plenty to do and see: hiking, rock-climbing, petroglyphs, petrified wood, desert flora and fauna, and a 13 mile highway loop for driving or biking. Wild burros run free in the park but we didn’t see any while we were there.

Half a billion years ago the region was under a vast ocean densely populated with Paleozoic Era marine life. More than 9,000 feet of limestone and other carbonate rocks formed out of this environment and remained buried deep beneath the Earth for millions of years. Later when the oceans receded due to the seabed rising, swamps appeared and disappeared, and for a while the area was heavily forested as evidenced by petrified wood found there. Ephemeral waters left behind gypsum and salt as they evaporated. At some point, oxidation of iron-bearing minerals in the sediments took place producing the reddish colors apparent in the canyon today. On top of all this (following the Law of Superposition), massive windblown sand dunes shifted over the region at a time when it resembled today’s Sahara Desert. The dunes themselves were eventually buried and hardened into layers of sandstone.

During the Laramide Orogeny tectonic forces deep within the Earth’s crust began to crumple the landscape as predecessors to the Pacific Plate collided and subducted with the North American Plate and caused the older Paleozoic limestone to heave above the younger Mesozoic sandstone.

Impressive example of cross-bedding: Red Rock Canyon  sandstone shows the effects of wind on the sand dunes from which it was formed.
Impressive example of cross-bedding: Red Rock Canyon sandstone shows the effects of wind on the sand dunes from which it was formed.Courtesy Mark Ryan
Known as the Keystone Thrust Fault, it’s one of the best visible examples of such a geological feature, due to the stark color difference between the rock units involved.

The canyon’s calico-colored cliffs and boulders also display some really fine examples of cross-bedding, which can form in environments where water or wind flows over sand or gravel beds. The sand dunes that existed at Red Rock during the Jurassic Period were such an environment. We hiked up the rocks for a spell, and although, it’s fairly steep in places, the rough sandstone surface provided a very secure footing.

So, if you’re out Vegas way, I recommend you take some time away from all the artificial glitz and glitter to drive out and blow some cash ($5 per private vehicle) to view some of the dazzling natural glitz abundant at Red Rock Canyon.

LINKS
Red Rock webcam
More on thrust faults
More on the Keystone Thrust Fault

Dec
11
2004

New research reported on by a team of scientist lead by The Georgia Institute of Technology in Nature this week suggest we may have to rethink our assumptions about sea floor production at spreading ridges.

Learn more.