... photography of a geological journey

Owens Valley is a nearly perfect rift valley, a divergent boundary in which both sides are moving apart. Many geologic and hydrologic features, which are characteristic of rift valleys, are evident in Owens Valley, including normal faulting, volcanism, and geothermal hot springs, to name a few. But Owens Valley is complex, and it should not be reduced to a schematic "textbook" rift valley; nevertheless, I attempt to present a simplified photo-tour of the geologic features of the valley, and I hope you find it interesting and informative.

The photos on this page were taken on a field trip in October 1997, as part of the Ge 11a course at Caltech. The statements on this page are mine and are believed to be correct, and they should be helpful in giving you a general idea of the processes at work in a rift valley such as Owens Valley; however, no responsibility is taken for the complete accuracy of any statement. If you have any questions or comments, please e-mail me.

You may click on any photo to see a larger image.

Red Rock Canyon, California





Six to eight million years ago, layers of sediments, a basaltic lava flow, and a landlocked lake covered what is now Red Rock Canyon, California; since that time, the lake has dried up, and much of the basalt and sediments have been eroded. Today, the remaining rock layers dip roughly toward the north. Photo 1 (looking to the east) shows pinkish sedimentary layers underneath a thick layer of heavily fractured and more lightly-colored volcanic tuff, which is younger than the sedimentary layers and formed from volcanic ash. Photo 2 (looking to the north) shows a layer of black basalt, above the other rock layers, which cooled from a recent (in geological time, anyway) basaltic lava flow. The basalt has eroded down and partially covers the rock layers below it. Photo 3 shows jointing in the sedimentary rocks, and Photo 4 shows two normal faults cutting through the sedimentary layers, with associated displacements on the order of 10-20 centimeters. Click on Photo 4 to see the faults and offsets indicated.

Fossil Falls




The rock under our feet at and near Fossil Falls was primarily basalt, with small quantities of glassy obsidian also visible. The basalt was laid down in a series of lava flows, which means that, in the not-so-distant geological past, this area was covered by a thick layer of hot, fluid basaltic lava. The basaltic rocks are mostly black or dark gray, although some are noticeably redder, and others have red "patches" in them; the redder the rocks, the more they have been oxidized.

At the Falls (Photo 6), we see evidence of rushing water at some time in the past, as a channel has been carved out of the rocks, and the rocks at the Falls are much more smooth than in surrounding areas (see Photos 5 and 7). 10,000 years ago, during the last glaciation, when the Sierra Nevadas were covered by glaciers, Owens Valley was a much wetter place; ice from the Sierras melted and flowed into Owens Valley, and because the elevation in Owens Valley drops to the South, water flowed from the northern end of the valley toward the south. Water would have rushed over the rocks at the falls, weathering and sanding and smoothing them. There are no "fossils" at Fossil Falls; rather, it is the Falls themselves which have been fossilized. During the present interglacial, Owens Valley has become much more arid, and water no longer flows at Fossil Falls.

The red cone in Photo 7 is one of the cinder cones from which lava once flowed, and the mountain range in the background in all three photos is the steep eastern escarpment of the Sierra Nevadas.

1872 Owens Valley Earthquake - Fault Scarp




This is the fault scarp from the great 1872 Owens Valley earthquake. This earthquake was the largest to occur off the San Andreas Fault, in California, in historic times, and it was felt over much of California and present-day Nevada. Magnitude is estimated to be in the range 7.6 < M < 8.0, and fault rupture extends from just south of Bishop to Olancha. This earthquake was the result of normal faulting, which should come as no surprise in a rift valley. Even after 125 years of erosion, the scarp is still very visible, even if it is not as fresh as it once was.

If you click on Photos 8 or 9, you will see images indicating the direction of relative motion. The side of the fault I was standing upon to take both those photos dropped roughly 15 feet relative to the opposite side. Some classmates of mine are even in Photo 8, to give some perspective on the extent of the rupture and displacement. In the background of Photo 8 are the Sierra Nevadas, and in the background of Photos 9 and 10 are the Alabama Hills.

Alabama Hills



Probably the most significant inconsistency in Owens Valley to the "textbook" rift valley is that of the Alabama Hills. The Alabama Hills are a line of low hills in the center of Owens Valley, near the town of Lone Pine. Normally, one would not expect such a feature in the middle of a rift valley. But also puzzling is that the granites of the Alabama Hills have a different composition than the surrounding granites. The granites in the boulders on either side of the Alabama Hills contain pink feldspars and are characterized by large chunks. These are the same granites that can be found in Mount Whitney and the Sierra Nevadas to the west. In the Alabama Hills, however, the plagioclase feldspars are more weathered, have smaller chunks, and have turned more to clay. Clearly, the boulders on the valley floor did not come from the Alabama Hills. It is reasonable to assume that the boulders on the valley floor, on either side of the Alabama Hills, originally came from Mount Whitney and the Sierra Nevadas. But how could rocks from Mount Whitney to the west get to the eastern side of the valley? The Alabama Hills are in the way, and boulders from Mount Whitney could not have crossed over them. The most likely explanation for this apparent inconsistency is that the Alabama Hills have only recently been thrust upwards, and that the granitic sediments east of the Alabama Hills were laid down there before the Alabama Hills were uplifted.

Photos 11 and 12 show the spheroidal weathering of granites in the Alabama Hills, a common site in the arid climates of the Desert Southwest.

Mount Whitney and Whitney Portal





Mount Whitney, at an elevation of 14,494 feet above sea level, is the highest point in the 48 contiguous states, and it lies in the Sierra Nevada Mountains. Photos 13, 14, and 15 were taken from our campsite soon after sunrise, and Photo 16 is taken from the town of Lone Pine, just below Whitney Portal. It's beautiful, but it sure was COLD!

McGee Creek Fault



McGee Creek runs down a U-shaped valley which was carved out by glaciers during past glaciations. The mound in the center of Photo 17 (Photo 17 was taken facing west) is a moraine that was deposited by a glacier, and Photo 18 (facing southwest) is taken just on the other side of that moraine. A fault cuts across the valley, and offset is visible in a relatively straight line. In Photo 18, the near side of the fault has dropped relative to the far side, and from the angle of the fault plane, we can tell that this is, once again, normal faulting. The total displacement may have occurred all at once, but more likely, it is the cumulative result of several seismic events. Note that the road has to jog to the left, in order to stay at the same height on both sides of the fault. Again, if you click on Photo 18, you will see an image indicating the relative direction of displacement, and you will also notice a car on the road where the road makes its jog to the left.

Hot Creek



This site is a geothermal hot spring. Here, water filters down cracks and faults from the Sierra Nevadas, until it nears the magma chamber several kilometers under the surface; there, the water gets heated, and it rises, finding its way back up to the surface through vents and other faults, and coming out as hot springs. All the rocks in the area were once rhyolites, but hot water has metamorphosed the white feldspars to clay. The patch of white rocks on the face of the cliff in Photo 20 is an exposed "pipe" through which hot water has travelled up to the surface in the past.

Mono Craters





Photo 21 is taken from the rim (tephra ring) of Panum Crater, looking south to the line of domes comprising the Mono Volcanic Chain. Photo 22 is a photo of the tephra ring of Panum Crater, taken from within the crater, with the Sierra Nevada mountains in the background. Panum Crater is a classic example of an explosion pit in which the subsequent lava plug (Photo 24, right) was not large enough to completely fill the initial tephra ring (Photo 24, left). The rock observed here is mostly rhylolite. Photo 23 shows an excellent example of flow bands of obsidian and pumice in the rhyolite.

Mono Lake





The unusual formations in Mono Lake are tufas. Tufa towers are formed naturally when rain water in the surrounding mountains seeps into the ground, dissolving calcium from the rocks. The rain water then flows under the lake, gets heated by the magma chamber under the lake, and rises to the lake bottom. Once the calcium-rich ground water flows up into the lake, the calcium bonds to carbonates in the water, and, as water evaporates, calcium carbonates precipitate out, attaching themselves and adding new material to the chimneys already forming around the spring. The tufa towers, then, are the limestone precipitates left in the chimneys by falling water levels. Since Los Angeles began diverting water from the streams that flow into Mono Lake, the lake level has dropped 45 feet, which has exposed many of these tufa formations.

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this page created by Aron Meltzner initiated 03 January 1998 last modified 06 August 1998