Red Hill near Fossil Falls, with the crest of the Sierra Nevada in the distance.
The Sierra Nevada is the largest single block of rock in the United
States. It takes the shape of a huge 400 mile long westward tilting
range reaching elevations exceeding 14,000 feet. As such, it acts as a
gigantic barrier to Pacific storms. The lands to the east are dry and
largely barren. One high mountain range after another, like the White
and Inyo Mountains, or the Panamints, capture what little precipitation
remains, so that Death Valley is left as the driest place on the
continent.
A few streams originate near the crest and flow into the Owens Valley.
For years these streams fed the Owens River which filled Owens Lake,
covering just over 100 square miles to a depth of 30 feet or so. From
there the water could only evaporate or sink into the ground. Today the
lake is dry, the victim of water diversions that sent Sierra water to
Los Angeles. The lake would have to fill to a depth of 200 feet before
spilling over into the next basin at China Lake. That would require much
more precipitation than happens in the present day.
Upstream portion of Fossil Falls
But the climate has not always been like it is today. At various times during the last 2 million years the world cooled, and glaciers grew in the Sierra Nevada, eventually covering as much as 30% of the range. The glaciers would melt and some 10% of the Sierra water would drain into Owens Lake and spill over into China Lake, eventually reaching Death Valley. Rivers once flowed across the barren desert.
The rivers were like a highway for life. At some point in time, they connected with the Colorado River and numerous species of fish entered the waterways: trout, chub, pupfish and many others established populations in the streams and lakes of the Sierra and eastern desert valleys. As the glaciers receded and disappeared, so did the rivers and lakes of the desert. The few fish populations that survived did so in springs and Sierra streams. For the most part, aquatic life withered away in the desert heat.
There was another element to the story. The extensional forces that broke up the crust and formed the desert valleys produced fault lines, and provided conduits for lava to reach the surface. Volcanoes formed in many areas of the desert, including impossibly large calderas like the one at Mammoth Lakes, but in other places, the volcanism was less explosive. South of Owens Lake, there were a number of basaltic lava flows extruded within the last 130,000 years or so. Some of them crossed and blocked the Owens River. The rivers developed channels across the lava flows, and in one place, the waters poured over a forty foot wall, forming a waterfall.
The waters carved a channel in the solid basalt, and swirling gravel and boulders carved deep potholes. Fossil Falls, just a short distance off of Highway 395 near Red Hill cinder cone is what remains of this now extinct river. It is a fascinating place to explore, and was one of our stops on our journey to Death Valley a few weeks ago.
There is little to suggest that aquatic life could survive here, but the potholes play host to a surprising survivor of wetter days. Fairy shrimp are small branchiopods that lay eggs that can survive long periods of dehydration. They lie in the sediment in the bottoms of potholes at Fossil Falls, and on the rare occasions that rain fall, water fills the potholes. This sets off a race for survival as the eggs hatch, and the organisms try to reach adulthood and reproduce before the pitiless sun dries up the water in the holes. It's a hard life, but they've survived this way for thousands of years.
It had rained a week before our arrival and water stood in a few of the potholes. I took a close look, and the small pools were teeming with life. I couldn't get any good pictures, but a video I took shows the action. There are longish gray shrimp and some kind of very small swimming creatures at the water's edge. It's is amazing to see life persisting in the most difficult of environments.
With appreciation to The Guzzler, take a look at a mudflow just south of Owens Lake on Highway 395 near the settlement of Dunmovin. There were some cloudbursts in the area last Thursday that caused some real problems, including a number of road closures. The video is from Jeff Bradshaw of Laguna Niguel.
For my students who started school this week, this is close to where we are going on our field trip in a few weeks!
The U.S. Geological Survey (and my department seismometer) is reporting a vigorous swarm of small and moderate quakes about seven miles south of Keeler, California. The swarm has included two 5+ magnitude shocks, and at least 22 events between magnitude 3 and 5. Smaller events number in the hundreds.
Keeler is a small village along the former shoreline of Owens Lake at the south end of the Owens Valley. The pictures provide some context: the Owens Valley is the first of the Basin and Range Province grabens east of the Sierra Nevada, with the White/Inyo Mountains forming the east side. The top picture shows the Sierra crest, including the peaks in the vicinity of Mt. Whitney, the tallest mountain in the lower 48 states. The bouldery Alabama Hills and the town of Lone Pine are in the bottom of the valley, center-left, and the Inyo Mountains form the right-side skyline. With the valley floor at 4,000 feet and the surrounding mountains ranging up to 14,000 feet, the valley is twice as deep as the Grand Canyon. Although the Owens River flows through the valley (sort of), it is a faulted graben, not a river-cut valley.
The second photo (from the same vantage point on the Cottonwood Lakes road) shows Owens Lake, the south end of the Inyo Mountains, and the domes and craters of the Coso Mountains Volcanic Field on the right. Owens Lake is one of the pluvial ice age lakes that formed when glacial meltwater from Sierra glaciers drained into the desert. Unlike most of the dry lakes across the Basin and Range, Owens Lake actually had water until the 1920's. Los Angeles diverted the streams that flowed into the lake and sent the water south through a massive aqueduct to the growing city. Keeler was a depot for silver and lead being mined high in the Inyo Mountains at the Cerro Gordo Mine in the late 1800's. Ores were carried down to the town by aerial tramway, and then loaded on a steamship to cross the lake to railroad station.
The epicenters of the swarm would be in about the center of the second photo. Why are there quakes here? As noted before, the entire valley is a fault graben, so quakes are not at all unusual. One of California's largest historical earthquakes, the 1872 Lone Pine earthquake (mag. 7.8 or so) happened just north of here. Swarms have happened in the local region in the past, including some magnitude 5 events in the 1990's.
The Coso Volcanic Field lies just to the south. A collection of basalt flows and rhyolite domes, it was last active around 40,000 years ago, though a few cones may be younger.
UPDATE: not of the earthquake, but of the Coso Volcanic Field. It might be an actively forming metamorphic core complex! In 2 to 4 million years, the detachment surface may be exposed. I always enjoy learning something I didn't know before...
UPDATE #2: Loads of info on the quake swarm on the SCSN Pages here. The largest quakes are showing right lateral focal plane solutions, which is in keeping with the regional structural trends on the Owens Valley floor. This strongly suggests to me that the quakes are tectonic and not related to any kind of volcanic activity (but I'm not claiming expertise in the matter).
UPDATE #3: Reports of sand boils on the Owens Lakebed (see the comments) have been confirmed by the SCSN and USGS office in Pasadena (personal communications, no link).
UPDATE #4: See down in the comments for a correction on the history of Keeler from Roger Vargo, who is the sometimes caretaker at Cerro Gordo. Thanks for the correction, I was operating off the memory of a field trip from 25 years ago.
