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!