Rainbow Basin: the Barstow Syncline (Shallow Thoughts)

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Sun, 03 Apr 2005

Rainbow Basin: the Barstow Syncline

We started the day at Zzyzx, south of Baker. I'd been told that there were lots of geologically interesting things to see there.

If so, we couldn't find them. There's a little cluster of buildings marking the Desert Research Center, but it doesn't seem to be open to casual visitors; rather, they do classes and tours by appointment. Zzyzx abuts the southwest end of Soda Dry Lake, so you can get good views of the dry lakebed (with a little water on it here and there, thanks to the very wet winter) and across it to Mojave Rd and the Kelso Dunes. Worth the 5 mile detour off the freeway? Well, no, not really. But Dave was happy to find a relatively windless place where we could fly model airplanes for a few minutes.

Fortunately, Zzyxz wasn't the target of the day; that honor fell to Rainbow Basin, a few miles north of Barstow on the road to Fort Irwin. We'd actually tried to go to Rainbow Basin once before while passing through Barstow, but got lost. This time we had a more detailed map, since Rainbow Basin occupies a whole chapter in Geology Underfoot, Southern California.

Except it turned out that map wasn't any better than the wide-scale auto club map. The problem is that when you're coming in from the northeast, there's an exit off I-15 for "Fort Irwin Rd", even though no such exit shows on any of the maps. Fort Irwin Rd. is the road all the maps show as leading to Rainbow Basin. So that's the road to take, right?

Well, it turns out that Fort Irwin Rd and the more westward Irwin Rd angle together to meet at a point well north of the Rainbow Basin turnoff, which is on Irwin Rd. Irwin Rd. is the road all the maps label as Fort Irwin Rd, while Fort Irwin Rd. doesn't exist on the maps at all. Confused yet?

Here's the secret: if you exit I-15 at Fort Irwin Rd, make a left when you get to Irwin Rd. and angle back toward Barstow. Drive for longer than you think you should, and Look for a dirt road going off to the right called Fossil Beds Rd, which has no signs whatsoever related to Rainbow Basin even though supposedly there's a sign for it if you're coming in the other direction. Once you find Fossil Beds Rd, you're on track, and there are signs for the rest of the way.

Is it worth bothering with all this? Absolutely! Geology Underfoot rightly recommends starting with the "scenic loop drive", a short, one lane, one way dirt road that looks a little rough but really shouldn't be a problem for any car (at least when dry). It winds down through narrow canyons composed of colorful highly tilted layers of mudstone and tuff, then up a little hill to a parking area which offers a panoramic view of the Barstow Syncline, where the rock layers have been warped by fault compression into a striking U-shaped depression in an action mimicking the larger scale raising of the Transverse Ranges north of the Los Angeles basin by the San Andreas fault.

Curiously, on an intensely crowded weekend, Rainbow Basin was almost deserted. At the Syncline parking area we joined one other vehicle, a white van belonging to the "Loma Linda Department of Natural Sciences (Geology and Biology)". We never did spot the Loma Lindans; presumably they were down in the syncline measuring strike and dip. I hope my class field trips turn out to be this interesting.

Geology Underfoot recommends following the scenic drive with a hike of Owl Canyon, from Rainbow Basin's camping area, so we did so. The Owl Canyon trail offers a chance to walk through the axis of the syncline, up a mostly-dry creekbed to a dry waterfall. The colors aren't as impressive as the layers visible from the scenic loop, but the more subtle colors are interesting: the book mentions the green mudstone all along the wash (green from weathering of volcanic ash, not from copper) but doesn't mention the strikingly colorful granites washed down into the canyon, reds and bright greens as well as greys and blacks.

Along the way, there's a short cave in the side of the canyon marking a tributary which runs in wet weather. The book recommends bringing flashlights if one wishes to explore the cave. Since we had only bought the book a day earlier, we weren't well prepared for that; fortunately, I had my little blue LED keychain flashlight clipped to my water bottle, which turned out to be fine since the cave was so short.

Rainbow Basin was an excellent conclusion to our Mojave desert trip. This well hidden pocket park is well worth a side trip if you're anywhere near Barstow and have any interest in geology, or just in a short scenic drive among colorful desert rocks. Assuming, of course, that you can find the road in.

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[ 22:31 Apr 03, 2005    More travel/mojave | permalink to this entry | ]

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