Revealing the Riddle of the Red Rocks

 It's pretty amazing the places that didn't get made into national parks. It's pretty amazing that tens of millions of people visit Las Vegas and never make it just a few miles west of the city limits to see an incredible place where the rocks are red, and the rocks are a bit of a riddle. The problem? The rocks on the top, the gray limestone seen on the distant ridges is 300 million years older than the red rocks underneath. They are out of proper order.

The red rocks are the Aztec Sandstone, a Jurassic aged sand dune deposit that is correlated with the Navajo Sandstone, found in national parks like Zion, Arches and Capitol Reef. They developed in an immense sand dune "sea" that once extended from Wyoming to Arizona to eastern California.

The red color comes from iron oxide (the mineral hematite, or natural rust) coating the sand grains. I haven't found a lot of agreement over whether the red staining is a secondary effect, or a primary feature of the sandstone.

In either case, the outcrops are colorful, in shades of white, pink, red and brown. The rock exposures also display beautiful crossbedding, the sloping layers representing the slip faces of the ancient dunes, frozen in time by calcite or other mineral cement. In many places the rocks are broken up as if they have been through a gigantic nutcracker.

Which, by the way, they have.

Faults run through the region, an earlier set representing intense compression related subduction off the western coast of North America, and a later set formed during the extension that led to the development of the Basin and Range Province. The compressional thrust faults had the effect of pushing the older limestone rocks up and over the younger Jurassic sandstone during the Sevier Orogeny towards the end of the Mesozoic Era (that's the one with the dinosaurs). There are several such faults in the area, but the best known is the Keystone Thrust.

The later normal faulting dropped the valley floors and lifted the mountains, exposing the older faults to view. Erosion has resulted in the spectacular outcrops that make up the conservation area we see today.

Red Rock Canyon National Conservation Area is a wonderful place to visit, whether you've blown all your money at the casinos and can't afford to do anything else (hold back $10 for park admission!), or if you came to Vegas for the expressed purpose of visiting this wonderland of rocks. It is a much better use of your time if you ask me!

Seeing Things Upside Down in the Red Rocks: What To Do When You Get Bored With Las Vegas

Bored in Las Vegas? Really? Okay, the town is such an aberration in the desert that one can hardly get bored, but my attention was really elsewhere as we tried to get ready to meet the people traveling with us through the western Colorado Plateau. It took only three hours to get our rental vehicles, and it took some wrangling to get the last person to the hotel from the airport, but by 4:30 we had everyone, and most of them were ready and willing to check out some geological sights west of town. We headed to Red Rock Canyon National Conservation Area.

I made an appropriate first impression by missing the turnoff to the park, and taking the crew on an impromptu crossing of the Spring Mountains. But good ole Captain Eagle-Eye Wrong-Way eventually got us back to the road we wanted, and we headed towards one of the more stunning sights in the Basin and Range Province.

The Keystone Thrust was a Cretaceous structure that developed during the Sevier Orogeny, involving a section of the Earth's crust being compressed and pushed over the adjoining rocks. Rocks brought up from the depths are often older, so at Red Rock Canyon NCA, 500+ million year old Cambrian Bonanza King Limestone got pushed up and over the younger Jurassic sediments called the Aztec Sandstone. The site pretty much defines the term "contrast". Dark limestone forms the high Wilson Cliffs, while bright colored sandstone livens up the Calico Hills

There was also a lot of green. For some reason lots of flowers were evident (despite the desert environment, we were at well over 4,000 feet in elevation). The plants had attracted all manner of bugs and beautiful hummingbirds (top picture).

From the high point on the park loop, we were treated to an awesome view of the imposing cliffs of the Spring Mountains and the Keystone Thrust.

 The rocks maybe weren't really upside down so much as out of order. But the lizard climbing on the big boulder of sandstone was definitely upside down. I wish I could climb rocks that way!

I also wish for an eventful trip this week (in a good way) as we make our way tomorrow to Peach Springs and a drive to the bottom of the Grand Canyon. More later!