Out of the Valley of Death: Dreams of the Water Times at Fossil Falls

The lands east of the Sierra Nevada are dry. The massive mountain wall of granitic rock captures the Pacific storms that reach California and wrings the moisture out, leaving barren deserts and culminating in the hottest spot in the world and the driest locality in North America: Death Valley. Rocks of course are superbly exposed in this landscape, but the overwhelming impression for most visitors is the dryness.

It wasn't always this way. Climate change happens on different scales. There is the very rapid climate change that we are enduring in the present day, where major changes are taking decades rather than centuries or millennia. And then there is the kind of change that happens on a time scale of tens of thousands of years. That has been happening in the eastern Sierra Nevada over the last two million years as the northern hemisphere alternated between cold wet periods and warmer stretches. These were the Pleistocene ice ages. Evidence for at least six glacial advances can be discerned in the rocks and sediments of the Sierra Nevada, but independent analysis of ocean core sediments suggests that at least a dozen glacial advances took place (larger events tended to erase the evidence of earlier but smaller events in land deposits).

And yet the rocks retain the memory of water. Or in non-anthropomorphic language, the rocks contain clear evidence of earlier periods of wetter climate. A popular stop for geology field trips in the eastern Sierra Nevada is Fossil Falls in the Coso volcanic field between Ridgecrest and Lone Pine. The attraction of the site isn't a fossil, but the evidence of a large flowing river in the desert.

The valleys east of the Sierra Nevada are there not there because of river erosion. They exist because the crust itself has been stretched to the breaking point, and faults have formed. Some blocks sank to form deep graben valleys, while other blocks remained elevated to form the high mountains (horsts). Previously existing river systems were disrupted and vast regions no longer drained to the sea. This area of interior drainage is called the Great Basin, and it extends from the Sierra Nevada to the Wasatch Front in the state of Utah.

During the wet and cold periods the glaciers didn't reach far down into the valleys east of the Sierra Crest. But they did melt, and the meltwaters collected in lakes in the bottom of the deep graben valleys. When the cold periods lasted long enough, the lakes would fill to overflowing and spill over into the next basin. Fossil Falls are situated between Owens Lake and China Lake, with the cinder cones, plug domes, and basaltic lava flows of the Coso volcanic field in between. Lava flows from cones like Red Hill (above) occasionally blocked the river that would sometimes flow between the two currently dry lakes (Owens Lake contained a thirty foot deep lake as recently as the 1920s, but water diversions to Los Angeles caused it to dry up; it would need to be several hundred feet deep before it could spill over again at Fossil Falls).

The strangely shaped rocks then originated as the Owens River flowed and spilled over the edge of the lava flow that stood in its path. The smallest irregularities in the basalt would cause swirls and eddies in the flow, and sand, gravel and pebbles would grind at the edges of the shallow basins, eroding and deepening them. Eventually they would become potholes, and some of the potholes at Fossil Falls are immense. At least one of them tunneled ten or twelve feet down and broke through the canyon wall (below), forming a climbing challenge for canyon explorers (I proved I could shimmy up the thing a decade or two ago, so I don't need to prove it anymore...).

There is life in the potholes. When rain fills some of them, eggs of fairy shrimp hatch and for a few short weeks the small arthropods live, grow, mate, and die, leaving their eggs to wait for the next wet year.

It is strange to stand at this ancient river bed and hear only the gusts of wind. One can travel in one's mind though, and start to hear the crashing waters, the verdant cottonwood trees rustling, and the sounds of animals coming to the river for a drink. There were mammoths at the time, and horses, and camels, along with the more familiar deer and pronghorn antelope. One might have spied a Sabertooth Cat, a Dire Wolf, or an American Lion lying in wait in the hope for a meal. In the latest times, humans hunted for game in this more equitable environment. Chips of obsidian and housing rings are still present.

2005 was an extraordinarily wet year, and storms were actively dumping water into the drainage upstream of Fossil Falls. That year was the one and only time I've ever seen water flow through the gorge. The little stream could never be mistaken for the torrent that once flowed through and carved the canyon, but it was beautiful to see an echo of the water times of the Owens River system.

Fossil Falls is on Bureau of Land Management lands, and has been "developed" as a recreation site, with a small parking lot, campsite, and restrooms. The trail to the fall is not long, about a quarter mile, but it has a few rough spots. Climbing around the potholes can be a little intimidating, but the views are great from the rim as well.

Strangers in a Strange Land: A River Runs Through It, or at least used to

"After three days in the desert fun
I was looking at a river bed
And the story it told of a river that flowed
Made me sad to think it was dead"

from A Horse with No Name by Dewey Bunnell

Oh, the songs of our youth. A Horse With No Name by America came out in the olden days of 1972, and was one of those songs that imprinted itself into my junior high psyche in such a way that it can never leave. I think they call it an earworm, known to drive people nuts, but it is a pleasant one for me. It was a bit of an anthem for us backpackers and young desert rats. The lyrics from the song popped into my head as we pulled up to the next stop on our Strangers in Strange Land tour of Death Valley and the surrounding desert region of eastern California.

For first-time visitors, pretty much everything about the desert is strange. For first year geology students, the mystery is deepened by that little bit of extra knowledge they possess that has them observing the rocks and surrounding mountains, trying to understand how this landscape might have developed.

So what was going on here? We had arrived at the eastern foot of the southern Sierra Nevada and parked in the midst of a lava flow from a cinder cone in the Coso Volcanic Field called Red Hill. The age is not precisely known, but it probably is less than 130,000 years old. The lava flow is covered by tan colored eolian (windblown) dust. Up to this point nothing seems particularly strange, but in the picture above, one can see a gap at the edge of the lava flow, a little bit to the right. Why is it there?

Having walked a quarter mile over rough lava surfaces, it was a bit of a surprise to come across this sage covered flat area that seemed to be composed only of sand and silt, with only a few scattered boulders of the basalt. Something was a bit off about this part of the lava flow.

A look ahead confirmed the odd nature of this stop (below). The lava flow had turned into an intricate labyrinth of deep holes and channels. Even if you barely know anything about lava flows, it is clear that lava doesn't do this sort of thing. This lava has clearly been scoured by a pretty large river, the deep rounded pits being potholes formed by swirling masses of pebbles and gravel. The name of our stop, Fossil Falls, more or less supports the contention that a river once flowed here.

But this is a desert. No rivers are found nearby, and the few streams that flow off the nearby slopes of the Sierra Nevada sink quickly into the gravel-rich alluvial fans long before reaching this site. Could the channel be the result of flash floods? It doesn't seem likely, because the channel upstream has not been cleansed of the easily eroded silt and sand for a very long time. The growth of brush in the old channel suggests stability.

There is a story here...until the 1920s, a large natural lake existed just north of Fossil Falls. It was called Owens Lake, and it was the natural sump for most of the streams and small rivers flowing off the eastern flank of the Sierra Nevada. Although the lake covered an area 8 miles by 12 miles, it was usually no more than 30 feet deep, and in the intense desert heat the water left only by evaporating. There could be no outlet unless the water reached a depth of 200 feet or so. If it spilled over the water would be directed downstream right towards Fossil Falls. The lake is mostly dry today because Los Angeles has diverted the water than once flowed into the basin.

Where did all the water come from? Clearly at some time in the past the climate was cooler and wetter than it is today. The glacial ice ages that affected the region during the last two million years provide a reasonable explanation. Glacial meltwater flowed through Mono Lake and the Owens River, filling up Owens Lake which in turn spilled over into other lake basins farther to the south. These bodies of water are called pluvial lakes.

The potholes are still active today, but in a different way. The rare precipitation events will occasionally leave water standing for weeks in some of them. The silt in the bottom contains the desiccated eggs of small delicate fairy shrimp. When they get wet, the shrimp hatch and grow quickly to maturity in a race to produce eggs before the pothole is dry again. I found a few of them warming up in a small pool that still contained water despite the dry year.

Still, seeing the ghosts of long gone and forgotten rivers is sort of sad. There is no crashing of water cascades, just the quiet breezes (or gales, if a storm is blowing through).  But there was a previous trip...2005 was a very wet year, and we were following on the heels of a major storm. When we reached the falls, I heard something I had never heard before. Water flowing in the ancient gorge! There was no mistaking these chocolate colored trickles with the big ice age rivers, but it was impressive to see anyway.

This is the joy of teaching geology! From small inconsistencies in a landscape come grand stories of climate change, glaciers, vast freshwater lakes, and fertile ground for the curiosity and imagination of our students.

paleomagnetism in rocks that provided unexpected proof of plate tectonics. James Hutton staring at a Roman fortification in Scotland that led to the recognition of geologic time. Nicolas Steno studying "devils tongues" and discovering the biologic origin of fossils.  Geology isn't just an academic discipline; it is an adventure pretty much like no other.

Fossil Falls can be found a few miles south of the Coso Junction Rest Area on Highway 395. Turn east on Cinder Road (just south of Red Hill, the prominent cinder cone next to the highway), and follow the signs on the gravel road about a mile to the recently improved parking area and trailhead (vault toilet and picnic tables available, and a small primitive campsite).

The Keeler Earthquake Swarm

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.