A Look Back at Ten Years of Geotripping: The Story Told by a Single Rock

I'm commemorating a decade of blogging by dredging the archives for some of my favorite posts. 2010 was a turbulent year. We were still in the depths of the Great Recession (at least in our area), my summer trip was cancelled for the only time in the last 29 years, we broke ground on our new Community Science Center (affordable only because of the recession and the drop in construction bids), and I posted 298 blog entries, my most productive year on Geotripper. A great many posts continued the Other California series, and a really strange political controversy over the California state rock serpentine accounted for many more(more on this in the next post). It was hard to choose, but my favorite post of the year was the story of a single rock...
From November 20, 2010:

Meet my new deskcrop! I was out on the last field trip of the year, a journey through the Diablo Range to the San Andreas fault and Pinnacles National Monument. We had a wonderful day, which we didn't exactly deserve or expect. It poured all night, and somehow the rain stopped at daybreak. We had a few showers during the day, but a big storm was brewing in northern California (four feet of snow expected in Lake Tahoe, for instance). Happily, the deluge didn't start until we arrived back in town, and it has been pouring ever since.

In between we were treated to a beautiful display of clouds and rainbows, and we had a full day learning about California's most famous fault, and a few others as well. I picked up one rock, though, which captured my imagination, and reminded me of why I fell in love with the science of geology so long ago. It's a porphyritic andesite that I picked up on the shoreline of San Luis Reservoir near Pacheco Pass in the Diablo Range. The mountains form the western boundary of the Great Valley of California for a distance of about 125 miles.

It's not a remarkable rock in and of itself. Andesite is one of the most common of volcanic rocks, found pretty much all over the Pacific Rim in places like the Cascades, the Japanese islands, Indonesia, and by incredible coincidence, the Andes! The story of this rock could be very straightforward; it could be as simple as: it erupted...the rock weathered a bit...and I picked it up.

But that isn't the whole story. Context is so important; I picked the rock up from a layer, seen below, that was exposed on the eastern flank of the Coast Ranges. It is a sedimentary conglomerate. Again the story could be fairly simple; conglomerate is a fairly common rock too. We could hypothesize that the rock journeyed a bit further from the volcano, down a river and the river flowed from the mountains onto an alluvial fan. Along the way, it was rounded off by bouncing against other rocks...then I picked it up.

It turns out that story doesn't quite work as a hypothesis either. This conglomerate has some odd features that tell us that it didn't form in a river. It is topped by a gray sandstone that is in turn covered by siltstone and shale. Above it is another layer of conglomerate that is covered by sandstone, siltstone and shale. This pattern is repeated over and over, until we have a sedimentary formation more than 20,000 feet thick (four miles)! The layers contain marine fossils; some are shells of snails and clams, but sometimes the rocks include shark teeth and the remains of giant marine reptiles like ichthyosaurs, plesiosaurs, and mosasaurs.

OK, but what in the world could be moving boulders and cobbles around on the sea floor? Isn't that one of those places where the water is calm all the time? Sometimes that is the case, but not here. These rocks accumulated in large river deltas extending into a shallow sea that lay off the coast of California in late Cretaceous time, the final period of the dinosaurs. Because of constant large earthquakes, the edges of the river deltas were unstable and were often shaken loose. The mass of rocks turned into turbulent chaotic masses flowing along the sea floor at 30 or 40 miles per hour. These violent events are called turbidity currents. The turbidity currents can carry rocks for many miles. As the flow slows down, the larger particles settle first, followed by the finer particles, and so on. The sedimentary beds become graded by grain size (graded beds).

But why earthquakes? And where did the lavas and magma come from? It turns out these things are related too. This story seems to grow more complicated by the moment! In Cretaceous time, there was no San Andreas fault, and there was a lot less of California, at least a California that could be seen from above sea level. A vast subduction zone lay offshore, a place where the Pacific Ocean crust was being pushed under the North American Continent. As the ocean crust was pushed deeper and deeper into the underlying mantle, it heated up, and assisted by the presence of water, melted into magmas that rose upwards through the crust. Some of the magma exploded and flowed out the surface forming andesitic volcanoes, but other magma chambers cooled slowly three or four miles down in the crust, forming crystalline igneous rocks like diorite, granodiorite, and granite. Those are the characteristic rocks of the Sierra Nevada batholith, exposed in places like Yosemite Valley, Tuolumne Meadows, and Sequoia/Kings Canyon National Park.

I've often stood on the edge of Yosemite Valley and looked at the vast exposures of granitic rock, and imagined the volcanoes that once stood above, miles higher. I even wrote an extensive web series about being under the volcano. In my mind I could stand on the flanks of the Mesozoic volcanoes, watching out for predatory dinosaurs and gazing at pterodactyls flying overhead. It took a lot of imagination, but today the feeling was a little more tangible. I was holding a piece of the volcano in my hand.

I love where my geologic journeys lead; there are lots of pretty spectacular places to see in our present world, but so many more incredible landscapes of the past. It was a good day in the Coast Ranges!

Dinosaurs, Volcanoes, Monsters of the Deep, and Other Stories Told by a Pile of Rocks. And Disneyland.

One of my most vivid childhood memories was Southern California Gas Company's Disneyland Night. My dad worked for the company at the time. Once a year the company rented Disneyland and practically every employee and their family showed up. It's hard to explain why this is so extraordinary, but let me try. Have you ever heard the expression "E ticket ride", referring to an event almost too exciting to bear? Disneyland used to require the purchase of a ticket book which was used to buy your way onto the rides. The A, B, C, and D tickets were for the boring slow rides like Storybook Land, It's a Small World, or the Swiss Family Robinson Tree. They were okay, but the E tickets were for the good stuff, mainly the Bobsleds. So why was Disneyland Night so incredible? They didn't dole out tickets that night. You could ride any ride you wanted, as many times as you wanted. For us kids, this was better than Christmas and Halloween combined.

On those long evenings, we would ride every ride possible, and around midnight we would be exhausted. Everything was starting to close up, but there was one last ride we could do...the train. It passed through the diorama of the Grand Canyon and then it passed onwards into the Primeval World. I'm pretty sure that every misconception I ever had about dinosaurs and ancient life was shaped by the scenes that passed before me in that dark tunnel. If you've never had the opportunity, someone (probably many, really) has it posted on YouTube (thank you, Dan Smith):


One of the associations that was imprinted on my mind was the T-Rex battling a Stegosaurus with an erupting volcano in the background. I look at the diorama today and see Apatosaurs lolling in swamps (they didn't), Tyrannosaurs standing like tripods (they didn't), and other misconceptions, but it was always the lavas in the distance behind the battling dinosaurs that I remember so well. So, what possible connection could there be between childhood memories of Disneyland and yesterday's class field trip to the Coast Ranges? Bear with me!

Our first stop of the day was at San Luis Reservoir, a major storage site for the California Water Project. Water is drawn from the Sacramento River Delta and pumped into the reservoir where it is eventually sent south through an extensive canal system. It is the largest "off-river" reservoir in the country. Shoreline erosion has removed the extensive coating of soil, exposing the underlying rocks, a unit known as the Panoche Formation, a complex of conglomerate, sandstone, silt, and claystone that was deposited in Late Cretaceous time, the final years of the Mesozoic, the dinosaur era.

The rocks seemingly defy explanation. They formed in thousands of feet of water, in the forearc basin that developed on the landward side of a vast subduction zone/trench system that existed on the west coast of North America for millions of years. The subduction zone was eventually replaced in central California by the San Andreas fault, a transform boundary between the Pacific and North American plates. The thing about these rocks is that on an ocean bottom one tends to expect to find mud and silt. Sand, pebbles, and boulders don't make sense. There are no strong currents on the ocean floor like there are in rivers. Or are there?

On river deltas and on the edge of the continental shelf where shallow ocean floor gives way to steeper slopes leading to abyssal depths sediments may be shaken loose, by earthquakes for instance. In this situation sediment gravity flows and turbidity currents form, fast-moving bottom-hugging masses of sediment moving very fast into deeper water. These masses are capable of considerable feats of underwater erosion, carving deep submarine canyons into the continental shelf. There are many examples of these along the present-day coast of California, the Monterey Canyon being one of the most famous.

Source: U.S. Geologic Survey

So, dinosaurs and volcanoes? The boulders in the Panoche Formation contain the occasional piece of granite derived from the deep erosion of the Sierra Nevada. The granite cobble is a fragment of what once were the magma chambers for a vast system of volcanoes that would have closely resembled the Andes or the Cascades. Yosemite Valley and the other exposures of granite across the Sierra Nevada were once situated miles beneath volcanoes. In Cretaceous time. Meaning dinosaurs once wandered the flanks of volcanoes right here in California!

That's kind of a stretch, isn't it? Is there actually any evidence of the actual volcanoes? And what about the dinosaurs?

The volcanoes are the easiest to prove. Most of the rocks in the photos above are volcanic in origin. They are the eroded pieces of lava flows that once adorned the summit ridges of the Sierra Nevada much as Lassen Peak and Mt. Shasta do today in the Cascades. It really stokes my imagination to pick up one of these rocks and to realize it started as a mass of molten rock that was erupted onto the flanks of a large stratovolcano off to the east. The lava flow was eventually eroded and removed, the bits and pieces being carried in a river and dumped onto a river delta at the edge of the continent. One day the edge of the continental shelf was shaken by an earthquake, and the chunk of rock disappeared into the depths, carried along by a turbulent mix of water and sediment. It came to rest on the deep ocean floor. Eventually intense compression folded and lifted up the rocks, and finally a last bit of soil washed away and the rocks were once again exposed to erosion and trampling by the feet of geologists.

Proving the dinosaurs were here is a bit harder, but it happened. In the 1930s, a young teenager from Gustine was exploring Del Puerto Canyon in the Coast Ranges looking for fossil shells. What he found instead were the remains of a Saurolophus, a duck-billed dinosaur. It was the first dinosaur fossil ever found in California. How much more exciting can that be? The dinosaur was apparently drowned in a river flood, and the carcass floated out to sea where it eventually sank to the seafloor. 

The great thing is, the fact that you can find an occasional dinosaur bone in these hills isn't even the best thing one can hope to discover. There were other creatures living in the sea, and they were terrifying. Al Bennison, the boy who found the dinosaur, also eventually discovered the remains of a Mosasaur.

The Mosasaurs were relatives of the varanid lizards, a group that also includes the Komodo Dragons that still live today in Indonesia. They were fearsome marine predators, swimming with flippers instead of clawed legs, perhaps even attacking and consuming sharks (or unwary geology professors). They reached lengths of more than 30 feet.

And that is the story told by a pile of rocks along a nearly empty reservoir in central California!

Plotosaurus is one of the genera of Mosasaurs. P. bennisoni was the species found in the California Coast Ranges.

For a description of some recent research on the conglomerates of the Panoche formation check out: http://www.searchanddiscovery.com/abstracts/html/2013/90162pacific/abstracts/green.htm

What Creature of the Great Valley Could Have Snacked on Velociraptors? This one...

I apologize for the quality of the photographs today; they are from my phone, which is all I had when our latest display specimen arrived in our department. It's an exciting addition to the collection. We have been making a concerted effort over the last decade to raise the quality of science education in our impoverished community, an effort supported by our community with the passage of a bond act that brought about the construction of the Science Community Center at Modesto Junior College. The facility is wonderful, with a new planetarium and a fully operational observatory, as well as a vastly expanded Great Valley Museum.

My goal during this decade long project has been to increase the recognition that our county has a rich history of discovery in the field of paleontology. The first dinosaur ever found in California was discovered in our county in 1936. It was a hadrosaur, a duck-billed dinosaur, and we are still awaiting the arrival of a specimen of that creature in our department.

But what arrived today was one of the most fascinating creatures to ever come out of the sand and silt of the Great Valley Group: a mosasaur. The mosasaurs were some of the most fearsome sea creatures of the Mesozoic era. They were not dinosaurs, but instead were more closely related to large lizards. The middle skull is our recently acquired short-faced bear (Arctodus simus), one of the largest carnivorous mammals ever to exist, while the dinky little skull on the right is an accurately scaled velociraptor!

Mosasaurs arrived late on the scene, during the mid-Cretaceous Period, possibly occupying the environmental niche of the recently extinct Ichthyosaurs which had dominated the Mesozoic seas since Triassic time. Mosasaurs resemble varanid lizards (like the Komodo Dragon) and the various species ranged in size from about 10 feet (3 meters) to as much as 57 feet (17.5 meters).

The young man who discovered the first dinosaur in California, Al Bennison, also discovered the first mosasaur in our state. As it was an entirely new species, it was named Plotosaurus bennisoni. His specimen was probably about 30 feet long. Not long after an even longer species was discovered, Plotosaurus tuckeri, which measured over 40 feet in length.

I wanted a display specimen that could communicate to the young visitors in our museum and Science Community Center the excitement of the paleontological heritage of the region they live in, and having a four foot long skull of a mosasaur will go a long way towards achieving that goal. It arrived today and I was thrilled to see it. Just the same it was a terrifying creature. If it had you in its jaws, you weren't going anywhere. If you look in the picture below, you can see a second set of teeth in the back of the jaw. It was literally like something from the Aliens movies.

The specimen, from Taylor-Made Fossils of Missouri, is not a Plotosaurus, but will suffice to show what the Mosasaurs were like. The definitive source of information about the California mosasaurs is the book Dinosaurs and other Mesozoic Reptiles of California by Richard Hilton (who taught at MJC for a time; he is currently at Sierra College). The illustration below is a scan of his idea of the appearance of the Plotosaurus bennisoni.

From Dinosaurs and other Mesozoic Reptiles of California, by Richard Hilton

If you ever are passing through the Modesto area, be sure to stop in on the west campus of Modesto Junior College and wander through the Science Community Center. Even though the museum is not slated to open for a few more months, there are many other displays throughout the complex, including our new seismometer, and very soon, a mosasaur skull on the third floor in the geology area!

What Story Can a Single Rock Tell? A Day in the Coast Ranges

Meet my new deskcrop! I was out on the last field trip of the year, a journey through the Diablo Range to the San Andreas fault and Pinnacles National Monument. We had a wonderful day, which we didn't exactly deserve or expect. It poured all night, and somehow the rain stopped at daybreak. We had a few showers during the day, but a big storm was brewing in northern California (four feet of snow expected in Lake Tahoe, for instance). Happily, the deluge didn't start until we arrived back in town, and it has been pouring ever since.

In between we were treated to a beautiful display of clouds and rainbows, and we had a full day learning about California's most famous fault, and a few others as well. I picked up one rock, though, which captured my imagination, and reminded me of why I fell in love with the science of geology so long ago. It's a porphyritic andesite that I picked up on the shoreline of San Luis Reservoir near Pacheco Pass in the Diablo Range. The mountains form the western boundary of the Great Valley of California for a distance of about 125 miles.

It's not a remarkable rock in and of itself. Andesite is one of the most common of volcanic rocks, found pretty much all over the Pacific Rim in places like the Cascades, the Japanese islands, Indonesia, and by incredible coincidence, the Andes! The story of this rock could be very straightforward; it could be as simple as: it erupted...the rock weathered a bit...and I picked it up.

But that isn't the whole story. Context is so important; I picked the rock up from a layer, seen below, that was exposed on the eastern flank of the Coast Ranges. It is a sedimentary conglomerate. Again the story could be fairly simple; conglomerate is a fairly common rock too. We could hypothesize that the rock journeyed a bit further from the volcano, down a river and the river flowed from the mountains onto an alluvial fan. Along the way, it was rounded off by bouncing against other rocks...then I picked it up.

It turns out that story doesn't quite work as a hypothesis either. This conglomerate has some odd features that tell us that it didn't form in a river. It is topped by a gray sandstone that is in turn covered by siltstone and shale. Above it is another layer of conglomerate that is covered by sandstone, siltstone and shale. This pattern is repeated over and over, until we have a sedimentary formation more than 20,000 feet thick (four miles)! The layers contain marine fossils; some are shells of snails and clams, but sometimes the rocks include shark teeth and the remains of giant marine reptiles like ichthyosaurs, plesiosaurs, and mosasaurs.

OK, but what in the world could be moving boulders and cobbles around on the sea floor? Isn't that one of those places where the water is calm all the time? Sometimes that is the case, but not here. These rocks accumulated in large river deltas extending into a shallow sea that lay off the coast of California in late Cretaceous time, the final period of the dinosaurs. Because of constant large earthquakes, the edges of the river deltas were unstable and were often shaken loose. The mass of rocks turned into turbulent chaotic masses flowing along the sea floor at 30 or 40 miles per hour. These violent events are called turbidity currents. The turbidity currents can carry rocks for many miles. As the flow slows down, the larger particles settle first, followed by the finer particles, and so on. The sedimentary beds become graded by grain size (graded beds).

But why earthquakes? And where did the lavas and magma come from? It turns out these things are related too. This story seems to grow more complicated by the moment! In Cretaceous time, there was no San Andreas fault, and there was a lot less of California, at least a California that could be seen from above sea level. A vast subduction zone lay offshore, a place where the Pacific Ocean crust was being pushed under the North American Continent. As the ocean crust was pushed deeper and deeper into the underlying mantle, it heated up, and assisted by the presence of water, melted into magmas that rose upwards through the crust. Some of the magma exploded and flowed out the surface forming andesitic volcanoes, but other magma chambers cooled slowly three or four miles down in the crust, forming crystalline igneous rocks like diorite, granodiorite, and granite. Those are the characteristic rocks of the Sierra Nevada batholith, exposed in places like Yosemite Valley, Tuolumne Meadows, and Sequoia/Kings Canyon National Park.

I've often stood on the edge of Yosemite Valley and looked at the vast exposures of granitic rock, and imagined the volcanoes that once stood above, miles higher. I even wrote an extensive web series about being under the volcano. In my mind I could stand on the flanks of the Mesozoic volcanoes, watching out for predatory dinosaurs and gazing at pterodactyls flying overhead. It took a lot of imagination, but today the feeling was a little more tangible. I was holding a piece of the volcano in my hand.

I love where my geologic journeys lead; there are lots of pretty spectacular places to see in our present world, but so many more incredible landscapes of the past. It was a good day in the Coast Ranges!

And The Old World Passed Away... The Geologic History of the Colorado Plateau

Hunting for words. It is sometimes hard to avoid using biblical metaphors when describing certain elements in the story of the earth. Whatever else you may feel about it, there is no doubt that much of the imagery can evoke powerful emotions: apocalypse, Armageddon, rivers flowing red with blood, a rain of fire and brimstone...God's judgement upon the transgressors.

Is the word catastrophe enough? Disaster? Yes, maybe disaster. In the original Greek, it means "bad star", presumably referring to the bad omens seen in astronomical phenomena like comets and meteor storms. Yes, maybe disaster is the word I am looking for. And a passage from Revelations 21:1 seems strangely appropriate: "And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away; and there was no more sea."

I've been working on (well, off and on) a geological exploration through the Colorado Plateau region. I had no idea it would go on for so long, and with so many entries (since July, with 48 posts so far; if you are a glutton for punishment you can start catching up with the story here). Sometimes you just start out and then find your subject matter is just so rich, and the Colorado Plateau is certainly rich. In my last post a few weeks ago, we had reached the end of the Cretaceous Period, right about 65 million years ago. And I hinted that everything would change. On the Colorado Plateau, everything changed in a huge way. And thus my search (above) for the right words, the right imagery.

Disaster. For many, the world did end at the close of the Cretaceous. Anywhere from half to two-thirds of the species of animals and plants of the world disappeared forever. The dinosaurs were the most familiar victims, but there were many others, including plants, plankton, marine invertebrates, large sea-going reptiles, and a number of mammals. Many of the survivors were freshwater vertebrates with low food needs (crocodiles and the like), or who could hibernate (mammals), which suggests a nearly instantaneous event that lasted just a few years (although, it should be noted, this is a contested view; some argue it lasted thousands or hundreds of thousands of years). The cause? A giant asteroid (the"bad star")? A lot of researchers think so; a great deal of evidence exists for this hypothesis. Massive volcanism? Certainly a lot of lava poured from the ground in India right about this time (the Deccan Traps). Changes of sea level? The arguments continue, but something happened, something profound.

Another huge change took place in the plateau that makes the biblical passage from Revelations particularly resonant: the seas left the region for the final time. In fact, the entire region began to rise and massive mountains formed around the margins. Ultimately the plateau may have been uplifted as much as three miles. And erosion began. Not just a little, but a vast quarrying of nearly two billion years of sediments. Thousands of cubic miles of rock and sand simply washed away. Given the high elevation of the region today, the massive destruction of rock is destined to continue for millions of years, and eventually all that will remain will be a low plain eroded into the most ancient continental rocks. In other words, we are fortunate to be living in the times we have, where we can see, understand (in our limited way), and appreciate the history of this fascinating region. It is humbling in a way to consider that all the special places of the plateau country, the Grand Canyon, Zion, Arches, Canyonlands, Capitol Reef, all of these places are ultimately temporary.

At the end of the Cretaceous Period, the old world did pass away, but a new world emerged from the ashes. There was a new landscape, one of lakes, mountains and plateaus. And there were a great many new animals inhabiting the ecosytem, totally new creatures that had taken advantage of the disappearance of the giant reptiles. It was the Cenozoic Era.

The story continues! The picture today is the Comb Ridge Monocline, a huge rip in the earth's crust that formed during the Laramide Orogeny early in the Cenozoic Era.

The Cretaceous Parks of the Colorado Plateau: The Mancos Sea

Ah, the Mancos Shale. Woe unto anyone who tries to foolishly drive across it after a rainstorm. Deep disappointment faces fools who try to build a highway or dwelling on the black clay. Frustration to anyone who tries to grow anything on it. And poor health to those who must drink of water that emanates from or passes through it, with its load of poisonous metals. A former colleague who had worked in the region during the uranium boom could only call it the "d----d Mancos Shale".

When the Cretaceous Seaway expanded from the north and south, it inundated the central part of the North American continent, dividing it in two. To the west, high mountains and volcanoes produced vast amounts of mud and silt that drifted into the open water beyond the shoreline sands (represented by the Dakota Sandstone). The organic-rich sediments ultimately accumulated to depths of thousands of feet. Numerous creatures lived in the waters, including the usual snails, clams and oysters, numerous kinds of fish and sharks, but the most interesting fossils include the billions of ammonites (best thought of as octopi with shells; the Pearly Nautilus is a modern relative), and giant mosasaurs, the sea-going varanid lizards (think of a Komodo Dragon with fins).

The clay-rich sediment absorbs water to an extraordinary degree, and swells when wet. It thus gets mucky, and roads cut through it become impassable. Buildings settle and crack on the unstable surface. The clay contains all manner of nasty metals like selenium, arsenic and mercury, which can be absorbed by crops, and contaminate water supplies. And yet, in the right circumstance, the Mancos is a beautiful rock to behold (as Silver Fox can attest).

At Capitol Reef National Park, the Mancos is revealed in cliffs and badlands as an intricate maze of gullies and slopes. In the pictures above, tilted layers of Mancos are found along the eastern boundary region of the park. Factory Butte is one of the premier landmarks in the Bureau of Land Management lands east of the park (and is the site of a controversy over land-use policies and off-road-vehicle use).

Mesa Verde National Park, famous for the Ancestral Pueblo Cliff Dwellings, is also a place where the Mancos is a prominent part of the scenery. More in future posts!

Oh, my former colleague? Many years ago, we convinced him to join us on a field trip that included stops in the Mancos. He was reluctant, but came along. At some point, the students found a nice slope of the clay, and they started climbing and then running down (we aren't necessarily describing mature behaviour, but we've all done it...). We thought it would contribute to Will's healing of his hatred of the Mancos if he actually had some fun on it, so we egged him on, and he climbed the slope and came barreling down at a high rate of speed. He lost his footing, and tumbled down, cutting up his leg.

Oh well....

The Cretaceous Parks of the Colorado Plateau: the Cedar Mountain Formation

Well, yeah, except that it isn't the Cedar Mountain Formation, and it's not on the Colorado Plateau, and it isn't a park of any kind. If I may explain, the Cedar Mountain Formation is an exceedingly important part of the geological history of the Colorado Plateau, being the only representative layer in the region dating from the early/middle Cretaceous Period. It has also turned out to be a treasure trove of fossils with a rich collection of dinosaurian and other species preserving a time when animals were mixing or being separated from related species in Europe and Asia. So it is really important and all, and every geology field trip should stop and have a look at it and take lots of pictures and stuff. Except that I haven't done so on all of my many trips onto the plateau.

Extensive work on the Cedar Mountain Formation does not seem to have begun until the early 1990's (compare to the Morrison Formation, which was being excavated for dinosaurs in the 1870's). Some two dozen dinosaur species have been found in the unit, including several sauropods, iguanadons, troodons, one of the earliest hadrosaurs (eolambia), and my personal favorites, deinonychus, utahraptor, tenontosaurus, and a zephyrosaurus. At different levels in the formation these dinosaurs share affinities with European faunas while others are related to faunas from Asia. These connections reveal the severing of North America from the former and the linking to the latter during early and middle Cretaceous time.

So what's with the picture above? It is an exposure of the Cloverly Formation near Bridger, Montana. The Cloverly is nearly contemporaneous with the Cedar Mountain Formation, and many of the fossils found within it are similar as well. And I have actually been there, and participated in a dinosaur dig that was a defining life event for me and many of my students. So a few posts will soon follow, describing what we did there back in 1994. Please excuse the somewhat diminished quality of the photography, as these are scans of slides that were taken by a grossly incompetent photographer (me) back in the dark days before digital imaging.

These stories will also serve as my contribution to this month's Accretionary Wedge, hosted by Dave Shumaker at Geology News. The topic of the month is our favorite places to do field work, and was this ever it!

More soon!

The REAL Jurassic Parks were really Cretaceous

As any knowledgeable fifth-grader could tell you, few of the dinosaurs in the movie Jurassic Park had anything to do with the Jurassic Period. Most of the species in the movie lived during the Cretaceous Period, many millions of years later, including the velociraptors, tyrannosaurs, triceratops, and the ornithomimus herd. Offhand the only Jurassic dinosaurs I can recall from the movie were the massive brachiosaurs that occupied just a few scenes. The premise (from the sequels anyway) of the animals living in some kind of ecologically balanced paradise would be unlikely at best. The mixing of predator and prey species from long separated periods would lead to disaster, as most of the species would have no evolved defenses to predator attack methods. And of course, the whole "reconstitute a dinosaur" from old dinosaur DNA mixed with frog DNA idea is a real stretch anyway, although interesting results are coming from research with wooly mammoth DNA.

In any case, we continue onwards on our march through the geology of the Colorado Plateau. Cretaceous sediments are an important part of the Colorado Plateau sequence, and they reveal a changing world, including new plants (the angiosperms), a host of diverse new dinosaur species and many other animals. At the end of the period, the dinosaurs (and many other species) disappeared forever and a new world emerged in the Plateau country. A final transgression and regression of a shallow sea was followed by widespread deformation of the crust, and the rise of the region above sea level. The most recent era, the Cenozoic, our own time period, was beginning.

The Cretaceous formations of the Colorado Plateau are not as colorful as the Jurassic and Triassic sediments, but several national parks and monuments have been established in areas containing Cretaceous sediments, and in some cases the scenery is quite spectacular. Grand Staircase-Escalante National Monument and Capitol Reef National Park are two of the more striking examples, but other parks that are not really known for their rocks are also notable, including Mesa Verde National Park, Chaco Culture National Historical Park, Hovenweep National Monument, and Canyons of the Ancients National Monument. Important formations include the Cedar Mountain Formation, the Dakota Sandstone, the Mancos Shale, and the Mesa Verde Group.

Today's photograph is a sunset view of Fajada Butte in Chaco Canyon, one of the eeriest (but not in the scary sense) parks I've ever visited on the Plateau. The rocks are part of the Mesa Verde Group.

More soon!