The better known Barringer Crater in Arizona is an excellent example of a simple crater, while Upheaval has multiple shock rings and the apparent remnants of a central peak, perhaps even a central ring mountain. It's comparable to large lunar impact structures such as Tycho, Copernicus, or even Mare Nectaris or Mare Orientale, while its Arizona sibling is more like a small crater such as Linne.
So why is it called Upheaval Dome, you ask? Well, originally it was thought to be a huge collapsed salt dome: a pocket of subterranean salt swells from the effects of water, warping the rocks around it, then the salt leaks out and the dome collapses under its own weight. There are lots of salt valleys in the Canyonlands area, and the mophology of impact craters wasn't understood until fairly recently, so this explanation made some sense at one time. However, it turns out that there isn't any salt under Upheaval, and there are traces of shattercones and other heat-shocked rock, as well as chemical traces consistent with an impacting body. Gene Shoemaker and others have studied Upheaval extensively, and the results all point fairly convincingly to an impact. The national park service, however, hasn't quite come around, and still presents the salt-dome theory alongside the impact crater theory, and the name remains "Upheaval Dome". Sigh.
Dave and I have visited Upheaval several times -- it's one of the places we keep coming back to, and it's spectacular every time. We've been inside once, when we hiked up from the Green River on our honeymoon, and have walked the short trail to the two overlooks on top several times. The last time, however, we noted that the overlook trail continues (though no park documents mention this -- they all show the trail stopping at the second overlook), and this time we wanted to see how far it goes.
We didn't find out. It continues for miles past the overlooks, marked by cairns (ever notice how park brochures and signs never mention cairns? Do they figure that anyone silly enough to want to go for a hike in a national park already knows they're trail markers?), giving one spectacular view after another, of Upheaval, or its runoff canyon leading to the Green River, or the Navajo sandstone domes comprising the southern end of Upheaval's second shock ring. We puttered around for several hours, hunting cairns up and down steep slickrock surfaces and along sandy washes, trying to scope out connections between this upper trail and the "Syncline Loop" trail, which circumnavigates Upheaval farther out, beyond the first shock ring, and connects with the lower trail that goes into its center.
But all good things must come to an end, so eventually we found our way back (via the Syncline Loop), paid a quick visit to the Green River Overlook and the spectacular Grandview Point (perhaps the most scenic spot in any national park), watched a minivan essay the torturous turns of the Schaefer trail (riding the brakes the whole way; understandable, when you look at the several thousand foot sheer dropoff on the outer edge of this narrow dirt road) then headed north to the town of Green River to set up for our assault on the Maze. Green River may not have a list of dining establishments to rival Moab, but it has a central location under the scenic Book Cliffs, plus one thing Moab lacks: cheap motels with wi-fi access.
[ 21:59 Sep 14, 2004 More travel/southpark | permalink to this entry | comments ]