Saturday, December 12, 2015

Geology Guide Training in a Geologic Paradise - Las Vegas, Nevada

Most folks who work in the great outdoors often view Las Vegas as a place to be avoided at all costs. It is often thought of as a slovenly, loathsome place where night owls crawl around looking for a quick buck. For sure, there is that side to "Sin City." But the location of Las Vegas is anything but loathsome, rather it is a landscape paradise. I was fortunate recently to be asked to give geology training to a group of guides who work for Pink Jeeps Las Vegas. You may know this company from its uniquely painted 4X4 jeeps around the Sedona area but they also have operations in Scottsdale and Grand Canyon. Take a look at some of the nearby features we learned about in the Red Rocks National Conservation Area and Valley of Fire State Park.

Red Rocks National Conservation Area


The Red Rocks area is situated to the west of Las Vegas in the Spring Mountains. I took this shot from the 24th floor of our hotel room looking west. Here, Jurassic-age Aztec Sandstone is overlain by the Cambrian Bonanza King Formation. This relationship is due to Sevier-age thrust faulting in the Western Cordillera between about 150 and 80 Ma.

 
Another 24th-floor shot but a bit farther south where a ridge of Kaibab Limestone in the forefront of the mountains partially blocks the view of the Aztec Sandstone. This ridge is generally in place and protrudes upwards to the east on the local dip.


The Aztec Sandstone from the Calico view area. The Aztec is a time equivalent of the Navajo Sandstone on the Colorado Plateau and the Nugget Sandstone in the central and northern Rockies. It was deposited in an eolian dune environment.


Much alluvium can be found at the mountain front and is dominantly composed of the early Paleozoic limestone class. Note that since the fan went inactive, it has been dissected down about 150 feet.


Great view of the thrust relationship between the older limestone rocks (grey background) which now sit above the younger red sandstone. The block that moved on the thrust was transported some 40 miles! Remember that this deformation occurred when these rocks were buried perhaps by a few miles of overlying material. Only the recent period of erosion has exposed what is seen here.


Paiute Indians once inhabited the area and this mescal pit attests to their presence here at Willow Springs.


The Aztec Sandstone has been flooded by subterranean fluids which leached iron staining off the individual sand grains. The transported iron was concentrated in other areas of the sandstone, giving the rocks a variable color.


Contact between the Aztec Sandstone above with the underlying Kayenta or Chinle formation (reddish slope). Both names have been used in this area.


Guides on our day trip to RRNCA include Chris D., Chris B., Jim C., and Debbie S. It was a great day.

Valley of Fire State Park



Sunrise from the 24th floor over Las Vegas. From here we drove north in I-15 to Valley of Fire State Park.


Walking in a slot canyon through the Aztec Sandstone.


Within the slot canyon are these fractures, infilled with harder cement material, likely silica cement. (NOTE: I RECEIVED A CORRECTION FROM Lu ZV THAT THESE ARE: deformation bands or granulation seams, that form from the rearrangement and/or crushing of the sandstone grains in response to tectonic stresses).


Nice textures in the sandstone.


Farther on, we see a Cretaceous age conglomerate. This package of sediment, which sits on top of the Aztec Sandstone was derived from the west in front of the Muddy Mountains thrust sheet. Thus this is a syn-tectonic deposit laid down during Sevier mountain building.


Close-up with a large class of Aztec Sandstone within it.
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On the way out, we noticed offset fracture fillings along a cross-bedded plane. (NOTE: I RECEIVED A CORRECTION FROM Lu ZV THAT THESE ARE: deformation bands or granulation seams, that form from the rearrangement and/or crushing of the sandstone grains in response to tectonic stresses).


Fantastic offset of fractures along a cross-bedded plane.


Differential coloring between fractures. Whoa!


At Atlatl Rock, we see darker colored Aztec Sandstone with numerous rock art elements.


Close-up at Atlatl rock.


WooHoo!


Lichen train in a pour-off. The lichens preferentially grows where the water runs down.


Rock art


Las Vegas is known for its human element but nearby is another world centered in nature and as rewarding as any Southwestern locale.


Why not?

Lake Mead National Recreation Area


Lake Mead NRA recently updated their official park brochure. Inside there were a few surprises.


First off, the map portion of the brochure reflects reality of the reservoir level. The shoreline is drawn with respect to the recent drought. Note how far the roads are from reservoir - this is the lower pool elevation. Thus, the drought has been institutionalized on park literature.


Who would have ever thought that the image and sayings of Edward Abbey would show up on a park brochure for a National Recreation Area formed by a dam! This is milestone and reflects changing attitudes in the Southwest. My thanks to the guides at Pink Jeeps - Las Vegas for inviting to come to their little slice of paradise and share in some of their geologic gems.

4 comments:

Dan McShane said...

I once had a 4 day conference in Vegas. By the end I was exhausted because at 4 or 5 I would dash out to the various geology wonders in every direction and see as much as I could until dark in late May. It is a great place for geology! And nice notice of the Abby quote.

Lu ZV said...

Hi!

The planar features are not fractures, but deformation bands (or granulation seams), they form due to rearrangement and crushing of the grains of the sandstone in response to tectonic stresses. Beautiful!

Wayne Ranney said...

Thanks to Lu ZV for correcting this part of the blog! Wayne

Dr. Jack Share said...

Fantastic photos and commentary! Can't wait to see.