"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
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?
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.
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.
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).