Former Seas and Oceans: Searching for the Past in the Great Valley

The world changes. It changes minute by minute as events happen in human society, the disasters, the eruptions (such as Sinabung this last weekend), the wildfires, the earthquakes. Other changes are more incremental, such as the rise of mountain ranges and their removal by the relentless forces of erosion. Given enough time, huge changes take place, but no one in the midst of these processes would ever notice a difference over the course of their lives.

Teaching geology and the earth sciences is often a challenge, especially when we talk about the history of planet Earth. The rocks on the slopes before us may look barren and innocuous, but huge events reveal themselves when we start observing them carefully. As a professor at a community college, my students are usually neophytes in the geological sciences. They are seeing the earth from a new never-before considered viewpoint.

I was on the road this last holiday weekend, introducing my students to the geology of Death Valley National Park. Some are currently in geology classes, some already had taken my courses, and some were entirely new to the science. Death Valley is a long drive from our campus, so we left on Thursday night to cover the 200 miles of the flat Great Valley, and to get a head start towards the desert. We camped at Kern River County Park outside of the town of Bakersfield, and at the foot of the southern Sierra Nevada.

After a cold night, we awoke to a panorama of barren grass covered hills with no rocks in sight. A layer of soil covers them all, except where roadcuts expose a small part. We talked in camp before leaving about how geologists see landscapes. Where a politician might see only city and county boundaries, geologists see provinces, regions with a unique geological history that contrasts with the areas around them. The Great Valley of California, for instance, is a vast 400 mile long trough that has been collecting eroded sediments from the Sierra Nevada and Coast Ranges. It's been going on for at least 140 million years, and the sediments have accumulated to depths as great as 50,000 feet. More recently, perhaps during only the last one or two million years, the land was uplifted and gently tilted, causing the sediments to start eroding again.

We further talked about how geologists organize the rocks they see into formations, members, and groups. We recognize that in specific environments (ocean bottom, river floodplain, delta, sand dune) specific kinds of rocks will accumulate, and we can recognize by a change in the rock that the environment changed at some time in the past. In other words, as one looks at a cliff, different layers with different rocks and different colors show how the depositional environment changed, such as a river flood plain being inundated by rising sea level, or becoming drier and changing to a desert with dunes and the like. These unique layers are called formations. Formations are distinguished by being mappable and by having precise definable contacts with other layers above and below. Thinner distinctive layers within a formation may be defined as members, while several closely related formations (such as desert dry lake salt layers and desert sand dune deposits formed adjacent to each other at about the same time) may be classed as a group.

At our locality along the Kern River, a shallow seaway once existed. Maybe that's not such a stretch, since a rise of sea level of only 300 feet would inundate the area again. The presence of the sea is indicated by silt and sandstone layers, and the presence of numerous fossils. 15-16 million years ago, in the Miocene epoch, this was an ocean teeming with life. The shoreline must have been relatively close by because the fossil assemblage includes an occasional bone of a horse or camel, indicating a carcass that floated out to sea after a flooded river overtook the animal. The animals preserved as fossils are whales, dolphins, seals, walrus relatives, manatee relatives, and more than two dozen species of shark. Sharks have rarely-preserved cartilage skeletons, but their teeth are species distinctive. The size of the teeth range from barely visible to monstrous daggers almost a foot long (from the gigantic Great White relative Megalodon).

The rock layer is called the Round Mountain Silt, a formation within the Temblor Group. The incredible accumulation of fossils at the locality has been something of a mystery; suggestions include a volcanic ash disaster (no evidence of volcanism nearby, though), red tide poisoning (perhaps, but no clear evidence), or a feeding ground of large sharks (but large sharks were among the dead as well). A more recent suggestion is that the bones and teeth accumulated over a long period of time (perhaps 700,000 years) at the bottom of a sediment-starved basin (a deep trough a little farther offshore; such basins exist today in Southern California around the Channel Islands). Whatever the reason, the idea of finding fossils for the first time in their lives held great appeal for the students!

They shot off up the hill and although finds weren't abundant, almost everyone found a fragment of bone or a small tooth. The strange rectangular tooth in the picture above was that of a manta-type ray.

It's clear that some people spend a great deal of time digging and collecting at the site (the hillside has a prominent ledge where the digging takes place. Two years ago, one of the "serious" diggers was there, and showed us one of his really excellent finds, seen below.

The largest tooth ever found by any of my students was probably this one from 2011 (below). The variety in shape and size is apparent from the selection seen in the photo.

One warning about hunting for fossils in the region. The south end of the Great Valley is prime habitat for the fungal spores that cause Valley Fever. It's a nasty disease that is caused when the spores (which are in the dusty soils) get into your lungs and reproduce. If you ever give it a shot, take precautions...it's not a disease to be trifled with.

We got in the vans and started over the hill (Tehachapi Pass) on our way to the Mojave Desert, and then onwards to Death Valley, where our explorations would really begin.

Treasures From the Earth in the Great Valley: What the heck was living here?

Standing on a barren hillside east of Bakersfield, one looks over a dry landscape peppered here and there with oil drilling rigs. Because of the recent rains, the grass is green, but roasted brown is normal for these badlands. It's hard, standing in this desert, to visualize that this was once a shallow sea, a sea that was filled with life. 15-16 million years ago, there were ancient species of clams, snails, fish, rays, sharks, dolphins, seals, sea lions, and whales. The nearby coastal plains were populated with horses, camels, primitive species of elephant, and predators who were the ancestors to today's large felines and canines.

The Great Valley began existence as a forearc basin between the volcanic range of the Ancestral Sierra Nevada, and the vast Cascadia trench and subduction zone that formed the western boundary of North America for much of the last two hundred million years. The shallow sea collected sediments from the rising mountains, and the basin floor subsided beneath the weight of the strata. Ultimately, the sediments in the basin reached a thickness of ten miles in the area around Bakersfield. Since a great deal of organic material was present in the rock, oil and natural gas accumulated in traps beneath folds and faults.

The are a few spots were animals died in profusion, or where their carcasses accumulated. One of these is exposed at Sharktooth Hill, a privately owned area where a layer, the Round Mountain Silt, included a 3-4 foot thick horizon full of fossils (collecting is allowed with a fee). A few other slopes provide the occasional sharktooth or bone fragments. The origin of the plentiful fossils has long been a source of speculation. Some of the most reasonable explanations involve "red tides", accumulations of algal toxins in the food chain, and turbidity currents, which may have gathered carcasses in specific areas of the seafloor.

There's no experience quite like finding a fossil for the first time. What child hasn't dug in his or her backyard in the hopes of finding prehistoric creatures? The small bit of fish vertebrae or the diminutive shark tooth might well be a Tyrannosaurus rex skeleton for all a student is concerned. It's a good way to start a field studies course.

We didn't find that gigantic tooth at the top of the post, by the way. There are folks who spend days and weeks digging in the ground for specimens. We met a gentlemen who has worked the site for three months. The tooth may very well be from a Carcharodon megalodon, the legendary Great White Shark relative that reached lengths of as much as 60 feet (18 meters). And no, they don't still exist in today's oceans, despite what the Discovery Channel tells you. Isn't a Great White enough in terms of terror?

Out of the Valley of Death: Cutting our (shark) teeth as new geologists

Ropy lenticular cloud, southern Sierra Nevada on the Kern River. Photo by Mrs. Geotripper.

Our recent adventure in Death Valley National Park had some preliminaries. One doesn't just go headlong into the Valley of Death without a bit of preparation. I'm not really talking about survival gear as we face some harsh savage desert, but more preparation of the mind to be able to comprehend the incomprehensible idea of nearly two billion years of geological history. The rock exposures at Death Valley can make geologists from more humid climates cry with awe at the barren naked rock.

Photo by Mrs. Geotripper.

But what if you are a beginning geology student with maybe five weeks of an introductory course under your belt? Approaching Death Valley without some background and context is just begging for absolute information overload. So it was that we quietly introduced our students to the world of geology in a gentle landscape.

We left the previous evening, driving for four hours through the southern San Joaquin Valley. I talk a lot about how interesting the geology is in my home turf, and it is, but frankly, it's as interesting to drive through it at night as it is in the daytime! Maybe even more interesting...

We set up camp late at night at Ming Lake in Kern River County Park. We awoke to a strange ropy looking lenticular cloud off to the east (top of the post), and held our first class in the field, discussing the geography of our journey. We would be passing through a sort of structural nexus of California, with six provinces within view this day: the Great Valley, the Sierra Nevada, the Coast Ranges, the Transverse Ranges, the Mojave Desert and the Basin and Range. We talked about how geologists view a new landscape, establishing the types of rocks, and organizing the layers into formations, members and groups. We discussed the rock we could see from our campsite, and what we might find as we looked at it more closely. We reviewed the fossils that might be discovered. And we talked about Valley Fever.

We had been camping at the base of Sharktooth Hill, and we would have a chance to search for fossils in a formation called the Round Mountain Silt. The silt was deposited in a shallow sea that had existed here for many tens of millions of years in Mesozoic and Cenozoic time. Though the seas were shallow, the sediments were deep in this region, exceeding 50,000 feet. About 20 million years ago, large numbers of sharks and sea-going mammals had died in the region, and their teeth and bones were widely distributed. The number of teeth discovered thus far on Sharktooth Hill proper number in the millions, but the land is privately held (occasional digs are offered through the Buena Vista Museum of Natural History in Bakersfield). We would instead check out some more limited exposures on public land nearby. Some diligent searching usually ends in a few exciting discoveries.

The search was tempered somewhat by the knowledge that the fungal spores that cause Valley Fever have detected in these soils. The students were very cautious about raising any dust, and some wore face masks.

After an hour, a number of students had made some exciting discoveries. For most of them, it was the first time that they had discovered a fossil in place. There are around two dozen species of shark teeth known from these beds, as well as the fragments of bone from marine mammals like dolphins, whales, seals, and large extinct manatee relatives. Upwards of 140 species have been recovered from these layers, making it one of the most significant paleontology localities in the state of California.

My discoveries were modest, a few shark teeth and the tooth of a ray or skate. I spent most of my time helping the others develop the "eye". This usually involves finding a tooth in place, and letting them know it is in an area of a couple of square yards. With the confidence of knowing the tooth is actually there, they usually find it in short order.

With our introduction to geological interpretation complete, we headed across the oil fields of Bakersfield towards Highway 58, Tehachapi Pass, and the Mojave Desert. We were headed towards one of California's greatest state parks, Red Rock Canyon. Our trip had begun in earnest.

Strangers in a Strange Land: Just Getting There is Half the Battle...

And getting back home is the other half....

Death Valley is a heck of a long way from pretty much anywhere. The nearest big city is Las Vegas, 120 miles distant. The small town of Ridgecrest and village of Lone Pine are around 100 miles to the west. From our school, the distance is 400 miles. We only had a holiday weekend to explore the park, so on Thursday evening we packed the vans and drove the first 200 miles in the dark to set up camp near Bakersfield at the south end of the Great Valley. When the sun came up the next day, we would have only 200 miles (with a number of interesting distractions) to get to the park. We would have two full days to explore as much of the park as possible, and then a few stops in the morning on Monday before starting the long road home.

The travelers were community college students, which meant it was a very diverse group of 37 people thrown together into what I like to call a temporary dysfunctional family. There were 'old' people like me, and teenagers, a number of veterans and survivors from last year's trip, and a great many geology neophytes. They were going to learn the basic principles of geology in what I consider the finest way possible: total immersion.

I have to say the nicest thing I can about the quality of these students. If you are a teacher, you know the attitude that students often have, the "teach me, I dare you" look. Enthusiasm is, um, sometimes a rare commodity. It turned out I received a big stack of "Roadside Geology of Northern and Central California" to give away. We were almost packed and ready to go, and I casually mentioned that the books were in the lab, free for the taking. The picture below shows how special these students were...

Luckily, no one was trampled to death.

We arrived at our camp along the Kern River in the southernmost Sierra Nevada near Sharktooth Hill and set up camp in the rapidly dropping temperatures. I know my readers from the northern climes will chuckle, but we Californians really take a beating when we suddenly have to emerge from our homes and cars and start existing at temperatures below freezing. It was cold and damp, too.

But morning came, we packed our gear, and prepared for our geological adventure. This trip was an introduction to how geologists observe the world, so we started at the beginning: we looked at the landscape around us and started asking the basic questions that the first geologists did:

1) What rocks are found here?
2) What processes are acting on these rocks?
3) How did these rocks form, and how did they end up looking the way they do?

What we could see in the low foothills of the Sierra Nevada is that these rocks were not very resistant to erosion. There were no bold cliffs of hard igneous or metamorphic rocks, just gentle soil covered slopes. These rocks were loosely cemented sediments, mostly sand, silt and clay. They were in nearly horizontal layers that allowed us to define the basic unit of geologists: the formation, a distinctive layer of rock that is mappable, and which has definable contacts with the layers above and below. We talked about where these layers might have formed, and how we could tell. The issue of fossils came up, so we were able to talk about how geologists have found some very interesting remains in these hills: some clams and snail shells, and the bones of dolphins, whales, seals, manatee-like species, and many kinds of shark teeth. Clearly, a shallow sea once existed in this place.

The first, and sometimes hardest step in understanding the geological history of a place is to realize how completely a landscape will change over time. 20 million years ago, the Sierra Nevada did not exist as the high mountain range it is today. There were no Coast Ranges off to the west. There was only a shallow sea with a shoreline off to the east. The layers exposed here in the low foothills are called the Temblor Formation and the Round Mountain Silt, and these formations are one of the most famous fossil sources in California.

Not too surprisingly, listening to the talk of fossils caught the attention of the students. It was clear they couldn't wait to see for themselves if there were still fossils to find on the slopes above our campground. We drove a mile down the road, and the great search began.

After a few moments the first bone fragments were found, and then a few shark teeth. Over the next hour, almost everyone had found something of interest. It was a good start to the trip. We climbed back into the vans and headed over the Sierra at Tehachapi Pass, and into the Mojave Desert. Now that we knew what a formation was, we needed to start looking into how we tell the story of a sequence of layers and the various events that happened to them. We were headed to Red Rock State Park to learn the process.

Full disclosure: these are some of the extraordinary teeth that we found last year. I forgot to snap a picture of the fossils we found this year...

Death Valley Days: The First Day - Racing the Wind (and the torrential downpours)

We actually left last night, but drove the length of the Central Valley in the dark to make today more interesting (trust me, it's better that way). We drove through an intense rainstorm, raced on ahead of it, and set up camp near Bakersfield, hunkering down to await the onslaught. It didn't come! It's not that there is no storm, it's huge. But it was tracking north, and not moving east, so we were dry all night, and had sun for most of the day.

First stop was in Neogene marine sediments at the south end of the Great Valley, which included an introduction to field geology and the idea of formations and environments of deposition (our students are mostly seeing geology in the field for the first time). How do you know a layer is marine? One clue is in the hand of the student above: fossils! Somehow, unsurprisingly, a place called Sharktooth Hill yielded up shark teeth (and a few fragments of seagoing mammals).

The second stop was one of California's wonderful state parks (threatened in the current budget mess): Red Rock Canyon State Park. The Neogene sediments here, 60 miles farther inland, are terrestrial in nature, suggesting that the shoreline of the Pacific Ocean was a lot farther east a few million years ago. The students worked at the idea dividing an outcrop into formations or members. The sun was shining, but we were beginning to realize that we were being stalked and pursued by ominous looking clouds on the horizon. So, like refugees in a disaster movie, we set off in the direction that seemed the least stormy: north.

In about 45 minutes we reached Fossil Falls. It isn't a place to find fossils, it's a place to search for Ice Age rivers that haven't existed for 12,000 years or more. The overflow from Pleistocene Owens Lake poured over the lip of a basalt cliff and formed a bizarre landscape of giant potholes and polished basalt. There was an ancient form of life present, but it was still living: fairy shrimp, surviving in a few drying pools at the bottom of some of the potholes.

There was also the evidence of the previous inhabitants of the region (below); they left behind shards of obsidian and some artwork, bragging of their exploits in hunting (or maybe hopeful thinking?)

The storm was intensifying to the north of us and from behind, and from the west. We turned east (which we were going to do anyway), and skirted the south end of Owens Lake. In the Ice Ages, it was hundreds of feet deep, and in modern times a lake 30 feet deep persisted with no outlet, but Los Angeles sealed the fate of the lake in the 1920s when they diverted the streams feeding into the Owens River and sent the water south.

The weather turned ever more ominous as we passed over the Inyo Mountains near old mining town of Darwin, but a thin beam of sunlight broke through the clouds and lit up a ridge of Paleozoic limestone along the crest of the mountains.

We careened down the Inyos into the Panamint Valley, driving right through the heart of a breached cinder cone in the process.

After being buzzed by an F-16 at only a few hundred feet, we crossed the bottom of Panamint Valley, and were treated with a marvelous view of Telescope Peak, which at 11,049 feet is the highest elevation in Death Valley National Park. We crossed Towne Pass in the Panamint Mountains (5,000 feet), and descended a vertical mile to our camp at Stovepipe Wells, elevation...0 feet. After spending an entire day worrying about the gigantic storm enveloping California, we had not had a single drop of rain. Looking at the weather radar, I don't think we will be so lucky tonight; a 100%chance of rain is in the forecast. We battened down the hatches, and snuggled in for a good night's sleep. Tomorrow the adventure continues!

The Other California: Sharktooth Hill and a Fossil Collection in Need of a Good Home

Besides the familiar La Brea Tar Pits (translation: "The Tar" Tar Pits), California is not widely known as a treasure trove of fossil discoveries. A little of bit of digging (pun intending) reveals the state as a rich resource of the history of life through time. Death Valley and other parts of the Basin and Range province have been a source of Proterozoic and Paleozoic fossils which are more varied and complete than the assemblage found at Grand Canyon. A few dinosaur bones have been found here and there, but the record of seagoing reptiles is (to me, anyway) even more intriguing: mosasaurs, plesiosaurs and ichthyosaurs. But if you ask paleontologists about the time period with the richest fossil record in California, they may very well mention the Miocene epoch of the Neogene period (5.3 to 23 million years before present). California has some of the thickest sedimentary sequences of Miocene rocks anywhere, including marine and terrestrial environments. A future post may include a discussion of the Ricardo and Barstow formations in the Mojave Desert, but for reasons to be noted in a moment, I want to talk about the Temblor Formation in the Central Valley and Coast Ranges. The Temblor is a sequence of sandstone and siltstone that was deposited in shallow basins offshore in Miocene time, around 15-16 million years ago. A member of the formation, the Round Mountain Silt, is one of the most productive fossil layers in the state.

During the Miocene epoch, the Pacific shoreline lay at the eastern margin of the southern San Joaquin Valley. To the east, where desert landscapes exist today, there was a semi-tropical savanna environment inhabited by camels, horses, tapirs, sloths and elephants. The shallow sea was home to nearly two dozen of species of dolphins, whales, pinnipeds (seals, sea lions and walruses) and other sea-going mammals, including a hippo-like creature called Desmostylus. The fauna also included turtles, crocodiles, and numerous birds. Something needed to fill the slot at the top of the food chain, and given the name of the locality, it isn't too surprisingly a group of sharks. Lots of them; about 27 species of sharks and rays have been discovered here, including the Discovery Channel's favorite, the massive Carcharodon megalodon.

The layers exposed at Sharktooth Hill (along the Kern River upstream of the town of Bakersfield) have yielded up not just thousands of specimens, but hundreds of thousands. In some places, a shovelful of dirt would have hundreds of teeth inside. Numerous studies have been undertaken at the site; a good review can be found here. The national significance of the site was recognized in 1976 as Sharktooth Hill was added to the United States Landmark Registry.

Sharktooth Hill is one of the most important fossil localities in the western United States, and one of the more important fossil collections to have come out of the hill is now being sold by the widow of an amateur paleontologist. The fossils in question have been on public display for a number of years at the CALM Zoo and more recently at the Buena Vista Museum of Natural History. They have hopes of getting the Allodesmus fossil (a primitive sea lion), but the price is too steep for their budget at around $150,000. I hope that some sort of arrangement can be made that will allow the fossil collection to remain accessible to the public. It is a great resource.

The Other California is my continuing series of what to see in our great state when you've visited all the really famous places that show up on all the postcards.