The Struggle for Life in a Harsh Desert: The Living Fossils of Fossil Falls

Fossil Falls, the Bureau of Land Management site near Little Lake and south of Owens Valley, is one of the strangest sights in the California Desert. The ironic point of Fossil Falls is that it has neither fossils, nor does it have falls. It is the former path of the glacial ice age Owens River where it drained Owens Lake and spilled over into China Lake Valley. The river was quite vigorous in its time, and carved a fascinatingly complex waterfall complete with giant potholes. But except for the occasional rill formed during rainstorms, the falls have been dry for thousands of years. I've written about the falls at length several times over the years (check out a sampling by clicking here).

But that's not what I wanted to talk about today. I want to talk about something I know practically nothing about (that's my right as a blogger!!). Every time we stop at Fossil Falls and the students are exploring the labyrinth of potholes and drop-offs, I am on my belly staring at a small hole in the lava flow. What could possibly be more interesting than volcanism and glaciers and faulting and the Sierra Nevada?

Well, nothing actually. But after visiting the site for thirty years, some other things can capture my attention...such as a desperate struggle to survive in a horrifically harsh land. In the small crucible of an insignificant pothole, an entire ecosystem has been born, and has only days to grow to adulthood, reproduce, and then die. The players are small arthropod shrimp, and maybe ostracods (seed shrimp).

Arthropods were one of the earliest forms of complex multi-celled life to leave a rich fossil record. Trilobites (the fossils of which we will see in a later post) account for around three-quarters of all of the hard-shelled fossils in rocks from 530 million years ago. The arthropod phylum, which includes the insects, spiders, scorpions, crabs, lobsters and many others, is the most successful lifeform ever to inhabit Earth, both in terms of biomass and in diversity. Arthropods are found in the deepest coldest oceans and in the hottest of rainforests. But one might expect that the desert would defeat them, especially those species which have gills, and thus must live in water to survive. But here at Fossil Falls there are creatures that have adapted to the severe climate. Their secret lies in patience and speed.

Desert Shrimp and Seed Shrimp (or Ostracods?) in close up.

I'm always struck by how these small creatures cling to life in their exceedingly small habitat. They are the extreme example of how life finds a way even in the most difficult of circumstances. No water most of the time? Evolve a way for the species to survive desiccation even if an individual cannot. Water for only a short time? Evolve rapid maturing and reproduction. Long periods of drought, possibly lasting for years? Evolve eggs (or cysts) that can last for years without water. These tiny beings can show a direct line of ancestry to the first arthropods in Paleozoic seas 540 million years ago, but they are very different creatures now.

These little creatures are actually bivalves in the manner of clams, but they are far different. The unfortunate ant provides scale.

I admit to not knowing very much about the species of creatures found in this hole, and an internet search didn't yield very much information. I hope my biologist readers can shed some light on the identities of these creatures. I will gladly add the info to this post. As best I can tell, the larger animals (below) are called Desert Shrimp. The extremely small yellow creatures seem to be either a Seed Shrimp (a Branchiopod), or an Ostracod.

This close up from a previous year shows a shrimp with an egg sac

I got a bit of video showing the ghostly Desert Shrimp and the really hyperactive Seed Shrimp. I guess they all have a lot to do, and not much time to do it in...

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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.

Where the River No Longer Runs, Life Persists: Fossil Falls in the Eastern Sierra Nevada

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.

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).

Fossil Falls

A bit more on Fossil Falls, which was the subject of Friday's Mystery Photo. The falls formed when Owens Lake overflowed during the Pleistocene ice ages. In 2005, we had the unusual pleasure of seeing water actually flowing through the gorge, as we had arrived on the heels of a pretty large storm. The water was rich with silt, giving it the latte-like appearance.

Althought the falls are almost always dry, a modern analogue is visible on the Rogue River in Oregon, just outside Crater Lake National Park. The Rogue River Gorge is a pullout on Highway 62 from Medford, about 7 miles from the park. The river flows through a breached basalt lava tube, and is actively forming potholes that are strikingly similar to Fossil Falls.

A Place Where Water Once Was But Was No Longer, But Once Again Was - Travels in Death Valley

I'm finally not "liveblogging the deluge" anymore. I thought back at the beginning of January that I was monitoring a historic flood event that was going to be over with in just a few days. Somehow, new storms kept blowing through, and I was watching and monitoring flood activity around the state. Those "few days" turned into a six-week series of observations. But now that the storm activity has subsided a bit, the observations are going to be in the past tense. I didn't have much in the way of internet access over the holiday weekend, and we went and stared into the abyss of the storm with little to defend us but waterproof jackets and the nylon walls of our tents. We explored Death Valley National Park during one of its most intense storms of the year.

On the whole, we were pretty lucky. We got drenched by rainstorms on the first two nights of the trip, and rain played havoc with our travel plans during the first two days, but most of the principle roads in and around Death Valley remained open, and we were able to get to most of our objectives. The first day was certainly typical of this; we missed a planned fossil hunt because of the driving rain, but we managed stops at the other three localities, and even added two extra stops that weren't in the original plans. Our first stop was at Red Rock Canyon State Park near Mojave for a look at the colorful terrestrial deposits of the Ricardo (or Dove Springs) formation. If the exposures look familiar, you've probably seen them in a number of Hollywood movies. I've written extensively about the geology of Red Rock in the past; check out this post for some details of this fascinating place.

The real thrill of the day was to see water where water once was but was no longer, but once again was. Shall I explain?

During the Pleistocene Ice Ages between 2 million and 12,000 years ago, the climate of the northern hemisphere swung wildly from warm to cold and back to warm again, perhaps as many as twenty times. Ice accumulated across broad swaths of Canada and northern Europe, and several times crept across the border of the United States, ultimately covering around 30% of the lower 48 states. The thick ice cap never reached Oregon or California, but the Cascades and the Sierra Nevada developed an extensive network of alpine glaciers. Some streams of ice, for instance in the Tuolumne River basin, reached a length of 40 miles.

The glaciers of the Sierra Nevada never reached far into the desert basins to the east, but the influence of the cooler and wetter conditions was unmistakable. Meltwater filled the enclosed basins which then spilled over into adjacent basins, forming a series of what are now called pluvial lakes. Mono Lake is a small remnant of the glacial Lake Russell, and Owens Lake still contained water as recently as the 1920s (before Los Angeles diverted the incoming streams). Other lakes included China Lake, Searles Lake, Panamint, and ultimately Lake Manly in Death Valley. Vigorous fast-flowing rivers connected the widely separated lakes. Our second stop concerned one of those rivers, the one that flowed from Owens Lake to China Lake through the Indian Wells Valley.

From several hundred thousand years to as recently as 10,000 years ago, basaltic lava flowed from cinder cones and fissures of the Coso Volcanic Field. Some of these flows blocked the river, and formed a forty-foot high waterfall. The river scoured a channel, and the waterfall eroded in an upstream direction. Boulders trapped in river eddies swirled around, forming amazingly deep potholes. And then the ice receded. The level of Owens Lake dropped below the rim, and the river through what we call Fossil Falls ended.

The river ended thousands of years ago, but on rare occasions there is an echo of the days when a wild river flowed through the gorge. I've seen it only twice, but when the rains have been plentiful in the Owens Valley, a small stream of water flows through Fossil Falls. That's what we got to witness last week, thanks to the Bombogenesis storm (or Lucifer, or whatever they called it). A river the color of a creamy latte made its way through dark basalts.

It was a fine introduction to our exploration of the geology of the Death Valley region, and it wasn't the first time we were going to see water in places where water was not normally found. Death Valley is a place where the water once was, but was no longer, but once again was...

This last picture is kind of cheat. I didn't climb down into the gorge for a close up, so this is from 2005, the only other time I've seen water at Fossil Falls.

The Islands of Interior California: The Littlest Islands of All

Red Hill with the southern Sierra Nevada in the distance

How often in life have you stepped back from the rat race and considered your life and your place in the cosmos? Wondered why you are here and what does it all mean? Do your conclusions and philosophy change over time? Or is life just such a rush that you deal with it, and look back and wonder where all the time went?

If there is one thing we learn as we delve into geology, it is that time is a relative thing. We look at someone a hundred years old, and we think of a century as a very long time. And yet a human lifetime is miniscule in the face of geologic time on earth. The world has existed for 45 million centuries. Whatever his other failings, Richard Dawkins put our existence into perspective nicely:

"After sleeping through a hundred million centuries we have finally opened our eyes on a sumptuous planet, sparkling with color, bountiful with life. Within decades we must close our eyes again. Isn’t it a noble, an enlightened way of spending our brief time in the sun, to work at understanding the universe and how we have come to wake up in it? This is how I answer when I am asked—as I am surprisingly often—why I bother to get up in the mornings." 

With that idea in mind, can you imagine how ancient we humans would look to a creature that lives an entire life within maybe three or four weeks? That's where we find ourselves today, within the smallest of California's "islands". By "islands", I'm referring to the isolated sources of water within one of the harshest deserts in the world, Death Valley and the surrounding Basin and Range Province.

Red Hill (top picture) is a cinder cone and associated basaltic lava flow situated between the Sierra Nevada and the Coso Range south of Owens Lake. The lavas are tens of thousands of years old, maybe even several hundred thousand. This area is desert today, but several times in the last two million years global cooling radically changed the climate in the region. Meltwater from the Sierra Nevada glaciers filled Mono Lake Basin and Owens Lake to overflowing, and the resulting river flowed south towards China Lake and ultimately to Death Valley.

Water is a rare phenomenon at Fossil Falls. This is a shot from several years ago on a very wet trip.

Lava spilled out across the valley floor and blocked the flow of the ancestral Owens River, and the river formed a 40 foot tall waterfall. Over time erosion attacked the lava, causing the lip of the fall to migrate upstream. Pebbles rolling in the current started grinding out potholes in the lava, some small, and some more than ten feet deep. When the climate warmed up during the last 10,000 years, the river dried up and only the potholes and abandoned waterfall remain. It's a fascinating place to explore.

But islands? The small potholes have their own kind of story, one of the persistence of life in the face of the harshest conditions imaginable. The potholes are natural collection sites, capturing windblown dust and silt as well as seeds and most importantly to this story, the eggs of small creatures, possibly carried in the mud adhering to the feet of birds. During storms water collects in some of the potholes (very small islands of water in the midst of a desert). I can imagine the birds finding water in the potholes and stopping for a drink, with the eggs washing off in the water...and eventually hatching.

Within these pools are complete ecosystems of creatures who must live their entire lives on a scale of a few weeks. It begins with birth when a pothole is filled with water and ends in death when the water evaporates. The creatures include small fairy shrimp and what I assume are ostracods, small bivalved crustaceans. These animals are the distant and yet direct descendants of the first complex forms of life that evolved on this planet some 500 million years ago, creatures like trilobites and sea scorpions. Their original ancestors were creatures of the sea, requiring water to survive. They still require water today, but water is a precious and rare commodity in the desert environment. To survive, these descendants evolved eggs that could survive years of desiccation in a harsh desert environment.

One could speculate in a slightly humorous vein that these creatures don't have a whole lot of time to consider their place in the cosmos, and don't have much of a chance to ask themselves why they exist when life is compressed to a few weeks at best. But consider how short our lives are in the face of vast time across the Universe. Are we all that much more aware of ourselves?

A Fairy Shrimp (carrying an egg sac). The "sesame seeds" are Ostracods, very small bivalved crustaceans who were in constant motion.

This is the first installment of a mini-blog series about the biological islands of interior California, an exploration of the geological conditions that allow life to survive in the harsh deserts in the vicinity of Death Valley National Park. Fossil Falls is readily accessible to travelers on Highway 395 between Ridgecrest/Inyokern and Lone Pine. The one mile gravel road is a few miles south of the rest area at Coso Junction and just north of Little Lake. The falls themselves are at the end of a quarter mile walk across the lava flow. A small and decidedly barren campground is nearby. In addition to the potholes and falls, explorers can also find petroglyphs and small shelters where Native Americans carved arrowheads and spear points from obsidian.

Friday's Mystery Photo Explained

I was gratified by the many responses to Friday's Mystery Photo, and all of you were partly right, in that the photo was in basalt. The picture was in fact taken at Fossil Falls near the Coso Range east of the Sierra Nevada (and south of Owens Lake). During the Pleistocene ice ages, Owens Lake filled with glacial meltwater, and spilled over into the valley to the south. The river poured over a thick basalt flow. With all manner of boulders and pebbles to work with, the swirling eddies produced a dazzling collection of huge potholes. The pothole in the picture was unusually deep and narrow, and eventually broke out into the main channel about 9 or 10 feet down. The more energetic and flexible members of our party could shimmy up the tube and climb out. I am about 15 years past being able to do it anymore!

The site is not far from the "village" of Olancha, and includes a small undeveloped campsite and restrooms. The falls area was popular with early Native Americans, with stone rings and obsidian work sites, as well as a few petroglyphs in the area. After rains, the potholes also play host to fairy shrimp, who are born, live, reproduce, and die within a period of a week or two.

Nearby Red Hill is a classic cinder cone, and numerous cinders and volcanic bombs can be found in the vicinity. The Sierra Crest provides a wonderful backdrop.

The pictures above reflect how reasonable the tree mold idea was. Tree molds form when lava flows inundate forests. The lava freezes around the tree trunks, and the trees then burn, leaving behind perfect molds. I have seen tree molds of big Ponderosa Pines on Medicine Lake Highland in northern California, and they are large enough and deep enough (10-15 feet) to climb into. The two molds in the second picture are two branches from one tree, and they merge about two feet down.

Pictures of Fossil Falls in the next post...

Northern Convergence: Finally Finding the Edge of North America at Yoho National Park...600 miles inland

Looking upstream on the Kicking Horse River at Field, B.C.

How strange geology is, and what wonderful journeys it provides for our imagination! So many geological processes are exceedingly slow, and yet over time incredible changes occur. How can I be talking about the edge of the continent when we are 1,000 kilometers (~600 miles) from the nearest shoreline?

I've called this narrative of our journey "Northern Convergence" because of the presence of a convergent plate boundary for the last 200 million years or so that has drastically altered and changed the continental margin of Canada and the Pacific Northwest. We had spent the previous four days traversing landscapes composed of exotic terranes, tracts of crust that originated someplace else and had been appended to the edge of the continent by way of subduction. The bits of crust were dragged into the trench, but were too buoyant to sink into the underlying mantle, so they mashed into continent instead, and intense deformation resulted. And the continent got bigger...lots bigger.

Looking downstream on the Kicking Horse River at Field, B.C.

We had crossed the Insular, Coastal, Intermontane and Omineca belts in our four days of driving, covering some 1,000 kilometers (600 miles), and we had finally reached the Canadian Rockies at Yoho National Park. It was here that we finally first encountered the ancestral edge of the North American continent. The limestone and and other sediments in the cliffs high above were deposited in a passive margin setting consisting of debris washed from the ancient continent around 900-400 million years ago. Everything west of our location was from someplace besides North America!

The scenery was on a truly grand scale. Yoho is contiguous with Banff National Park, and yet is rarely mentioned in the same breath (it's always "Banff and Jasper", maybe because they're on the Alberta side, and Alberta knows P.R.). Yet the park is spectacular, and even better, holds a treasure of worldwide significance.

The park protects mainly the upper watershed of the Kicking Horse River which includes several major icefields, including the Waputik and Wapta. The glaciers coming off the icefields contain finely ground silt and clay that stay suspended in the turbulent water. The rivers look like flowing milk at times.

Glacial "milk" also changes the appearance of lakes. In the calm water some of the clay begins to settle out forming a translucent turquoise color that is very striking. We made a stop at Emerald Lake to talk about the glaciers and have a look at the high ridge where the Burgess Shale was exposed.

Another road reaches up into the Yoho River drainage, providing access to Takakkaw Falls, the third highest in Canada at 254 meters (833 feet). The waterfall is a textbook example of a hanging valley, resulting when the main trunk glacier carved a deeper valley than the tributary glacier. The glacier feeding Takakkaw Falls is only a kilometer or so upstream of the brink.

If you need a sense of scale regarding 254 meters, look at the picture above where the water leaps outward from the cliff near the top of the waterfall. Let's zoom in on it. Those little dots to the left? Rock climbers!

All in all, Yoho National Parks is one of the most dramatic landscapes imaginable, but it's the rocks themselves that hold the real treasure. Although mining took place here last century, the treasure is in the fossils found in these rocks. About half of our crew were not with us as we toured the park, as they had left early in the morning to complete a tortuous 12 mile hike to see the quarry where the Burgess Shale fauna was discovered more than a century ago.

There is a problem with understanding the ecosystems that existed millions of years ago. Usually only the shells and bones are found, but the vast majority of organisms had soft bodies that are rarely preserved as fossils. They would invariably decay quickly. Fossil localities with the remains of soft-bodied organisms are few and precious, and our students were investigating one of the world's most famous. The Burgess Shale preserves the fossils of soft-bodied organisms that were present only a few million years after the dawn of complex multi-celled lifeforms.

How did they come to be preserved here? Just over 500 million years ago, the region was at the edge of the continent in relatively shallow water at the edge of the continental shelf. The shelf was unstable and occasionally a mass of mud would break off and sink into deeper water, carrying with it the organisms that were living there. The blocks sank into oxygen-starved water where the bacteria that would have consumed the soft body tissue could not survive. Mud covered and preserved the dead organisms. More than a hundred species have been described here.

The fossil quarry lies high on a ridge above Emerald Lake between Field and Wapta peaks. You can pick it out in the picture below, as the horizontal gash in the hillside with the lowest patch of snow. The hike is not easy, really an all-day affair. The quarry is a World Heritage Site and access is strongly restricted, and obviously collecting is not allowed. I've heard they've even gone after fossil sellers active on E-Bay.

I did the hike in 2005, so I didn't try it this time, opting instead to let my fellow professor hike with the students (she might forgive me the blisters one of these days...). The hike was one of the great adventures of my life, though, and I described it in detail in a post last April: you can read it by clicking here. There just aren't many times in life when you can be so close to the ancient past.

Holding a specimen of Marrella splendens in the Burgess Shale quarry, 2005

We visited with the local wildlife, and then headed over Kicking Horse Pass into Banff National Park. More adventures lay ahead!

A Black-billed Magpie (Pica hudsonia) at Field, B.C.

I hope that somebody appreciates that I made it through an entire post about a place named "Yoho" with nary a single "Pirates of the Caribbean" joke.