Boar's Tusk!

Following up on yesterday's post and Callan's rad red desert gigapan, I thought I'd share a couple more shots, this time of the Boar's Tusk and a little of the Killpecker dune field.  If you ever find yourself along Highway 191, you'll be driving right alongside a pretty phenomenal little bit of the high desert that, in addition to some slick geology, is also full of nice scenery.  I'd just caution, however, that if you DO decide to drive on the BLM roads, make sure you've got a vehicle with good clearance and four-wheel drive...it can get a little dicey!

Anyway, a prominent feature in the area is the Boar's Tusk.  Just like the more famous Devil's Tower, this pinnacle is a Pleistocene-aged volcanic neck that marks the formerly active volcanic fields of the area.  It's about 400 feet tall, and is a favorite nest-building site for hawks in the area.  












There's a steep little path up to the saddle, but like all volcanic terrain, a fall here can really hurt, so do be careful.








 



Here's a view, from the saddle, looking south towards White Mountain (the low plateau to the right).








 
 
And here's a view looking north, into Killpecker dunes, which is one of the largest active dune fields in the region.  Although it's pretty from a distance, the dunes are infested with 4-wheelers and ATVs and the associated jackassery that goes along with it.















Nothin' TOO spectacular, rock wise, but there's some all-right volcanic stuff to look at, IF that's your thing...

 
 The Boar's Tusk has also lent it's name to a beer available at the Bittercreek Brewpub in Rock Springs, WY.

Death Valley Day 4: Ubehebe Crater and Race Track Playa

Heading towards exposures of the Devonian and Ordovician in the north end of the park, we stopped off at some of the more tourist-y stops in Death Valley, including Ubehebe Crater and Race Track Playa. There were a fair amount of gawkers, of course, but the geology was pretty slick nonetheless.

Ubehebe crater is part of a chain of 13-16 craters recording Holocene (~6000 years, I think) phreatic volcanism in the region. In addition to the craters proper, base surge deposits can be found in relatively close proximity to the craters, and preserve some phenomenal flow structures.

The picture below was taken from a lookout along the rim of the crater, and shows the fine-grained lacustrine and coarser conglomerate deposits through which the volcano punched. The darker, banded unit that forms the rim proper (and shows an angular discordance with the underlying sediment) are tuffaceous beds with lots of pumice and basalt shards.

To the south of the main crater is Little Hebe, shown in the picture below. It is one of the younger craters, and shows evidence for effusive basalt flows (the rim of this crater is basalt, rather than the base surge deposits seen in the main crater).

If you head south of little hebe, off the beaten path, you will come across some phenomenal sedimentary structures, formed by the high concentration surge deposits as they flowed away from volcano. The picture below shows antidune cross-stratification, a fairly rare sedimentary structure produced by upper flow regime conditions and rapid deposition.

After Ubehebe, we sped northwards towards Racetrack Playa, probably one of the more famous spots in the park. Playa lakes, of course, are known for being FLAT ephemeral ponds, and are often evaporitic in nature; what is unique about Racetrack Playa, however, is that it is not a terminal playa. Rather than being found at the low point in the valley, Racetrack is actually 3000+ meters up in the mountains. There are no evaporite minerals (or casts) to be found in this playa; just a lot of (potentially thixotropic) mud and silt.

That, and the famous moving rocks.

There is still some debate as to what process exactly is responsible for moving these stones. Wind is a favorite explanation, but I would point out that if you look at the picture below, you’ll see a preferred orientation for many of the tracks, as well as a marked similarity in the angle of the changes in their direction. Also, the vast majority of these rocks are sourced from a north-facing prominence of basement rock exposed on the edge of the playa. Given the north-oriented face, 3000+ meter elevation, and the uniform nature of the tracks seen on the edge, we wondered if ice might not play an important role in the entrainment of these blocks.

Coming up next…more Paleozoic Carbonates!