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!

Rhyolite in the California Coast Ranges? And Happy Thanksgiving...

I only provided one picture of Pinnacles National Monument in California's Coast Ranges in my previous post, and it showed none of the scenery that makes the park a special place. So here are two views of the 22 million-year-old rhyolite composite volcano that was erupted, sliced in half by the San Andreas fault, faulted into a graben structure, exhumed by uplift, and eroded by water and wind and mass-wasting into a beautiful parkland.

The first photo is a view from the High Peaks Trail, a marvelous 5 mile loop through the heart of the park. The walk across the ridgeline is just stunning. In many places, footholds had to be scooped out of the rock to provide access, although the exposure level is not too frightening (nothing like Angels Landing in Zion, for instance). On a clear day, the far ridges extend forever into the distance, while the giant monoliths of rhyolite dominate the foreground. This hike, along with the trail to Delicate Arch, and the climb of Angels Landing, is one of my favorite hikes in the world.

The second shot is a view of the previously mentioned high peaks from the perspective of the south end of the park on the trail to the Chalone Peaks. The High Peaks Trail winds along the spine of the ridge in the center of the photo, and has connecting points to trailheads on both sides of the park (no roads cross the park, so one must choose to visit from the west or the east side).

The third photo is one of the wild denizens of the park, an old Tom Turkey. I have a feeling this bird would have issues with a certain recent vice-presidential candidate. I have seen a lot of wildlife in the park, include a huge flock of wild turkeys, four or five California Condors, huge numbers of woodpeckers, the standard deer and various rodents, and my favorite, a huge bobcat. The cat was hanging out near the edge of the campground near the road, and as we approached on the highway, what I thought was a feral kitty-cat seemed to grow larger and larger until I finally realized what it was and grabbed for my camera. Too late of course. And I can't help but look for the cat at the same spot every time I pass by during subsequent trips, camera ready in hand.

I hope everyone in the geoblogosphere has a fine Thanksgiving, even if you are not in the particular country that celebrates the day. Times are toughening up for many of us, but here's wishing that we all weather the storm, and that the job situation brightens for those of you who are between jobs and searching for employment. Best wishes to all of you.

When Rhyolite Breccia makes more sense than Granite

Breccia? You betcha! Looking for Detachment has a fondness for breccias, and mentions a few others who think likewise. My field trip season never seemed to end this year (that's not a complaint), as I had two lab field trips to see the Del Puerto Canyon ophiolite this week, and a Saturday field trip to Pinnacles National Monument in the California Coast Ranges. It was a great trip for breccia bloviating.

Pinnacles is a marvelous, if widely unrecognized little park about 30 miles south of the town of Hollister. It was established as a national monument in 1908 by Teddy Roosevelt for the tower-like peaks of rhyolite lava flows and breccias that are quite out of character with the normally rounded hills of the Coast Ranges. Those who sponsored the park for protection were unaware of the deeper geological significance of the park.

The great San Francisco Earthquake of 1906 brought worldwide attention to the San Andreas fault. Extending from the Imperial Valley of southern California to Mendocino on the northern California coast, it is one of the more extensive fault systems on the globe, and it has generated two major historical quakes (1906 and 1857), and a more recent "moderate" quake (Loma Prieta in 1989). Paleoseismicity studies have revealed dozens of major earthquakes during the last few thousand years.

Prior to the advent of plate tectonics theory in the 1960's, large scale lateral movements were not considered possible on faults like the San Andreas, though it was clear that the most recent movements had indeed been lateral. A seminal paper in 1953 by Hill and Dibblee argued that the fault had shifted hundreds of miles since Cretaceous time, a highly controversial assertion for the time. In the decades that followed, the San Andreas came to be understood as a continental transform boundary between the North American and Pacific Plates. Still, the fault researchers hoped to find an unequivocal piercing point that would allow a direct measure of the exact amount of movement on the fault.

The Pinnacles volcano was a rhyolite composite cone that happened to erupt on the San Andreas fault about 22 million years ago. The San Andreas ripped the volcano apart, and the two halves began moving apart, 10 or 15 feet at a time during large earthquakes. In 1976, V. Matthews demonstrated that the Pinnacles rocks were virtually identical to the Neenach Volcanics in the Transverse Ranges of Southern California. The two halves were separated by 195 miles!

The park has a lot of offer visitors. An extensive trail system bisects the park, including two sections that explore underground caves formed by boulders piling into the narrow slot canyons carved into the rhyolite. The vertical rock faces are a climber's paradise, as shown in the photo above. The rhyolite breccia (formed from volcanic mudflows, also known as lahars) makes for lots and lots of toe-holds!

I once was privileged to introduce the famous rock-climber Royal Robbins when he spoke to a group of geology teachers in Modesto. I made a point that geologists know a great deal about the properties of rocks, but how many of us stake our lives on our understanding of those rocks? Rock climbers do that every day...

Hill, M.L. and Dibblee, T.W. Jr., 1953, San Andreas, Garlock, and Big Pine faults, California - A Study of the character, history and tectonic significance of their displacements: Geological Society of America Bulletin, volume 64, pp. 443-458.

Matthews, V., 1976, Correlation of Pinnacles and Neenach volcanic formations and their bearing on San Andreas Fault problems AAPG Bulletin 60: 2128-2141

Rocks fall in Yosemite: Park Service closes 1/3 of Curry Village

Via the Yosemite Blog, the National Park Service has decided to permanently close down about a third of the tent cabins and other facilities in the Curry Village area of Yosemite Valley. The decision follows a series of rock falls over the last few years that have killed or injured several people. Investigations are seeking an explanation for an increase in incidents below the cliffs of the Glacier Point area.

The photo of the day shows some of the trees at Happy Isles that were snapped off by a huge rock fall in 1996 that killed one person and damaged the Nature Center.

Rocks fall in Yosemite? I had no idea that could happen!

I had one of those nice "convergence" moments today...I was discussing mass wasting in my physical geology classes today, and this story showed up on the front page of my local paper concerning the danger of rock falls in Yosemite Valley.

There was a rather nasty mass wasting event in the valley last month, and it has been noted that there have been four times as many rockfalls since 1996 than in the previous 139 (although I seriously wonder if this is because more attention is being paid to such events in recent years). If this is a true increase in the number of incidents, then the speculation that human interference is a causitive factor needs to be investigated. Most of the attention centers on water use at Glacier Point, the spectacular overlook on the rim of the valley. Some of the recent events have occurred in summer when visitation (and therefore water use) at the point is highest. Other researchers, including the park geologist, disagree with the contention that water plays a part in the recent events.

The other controversy concerns the placement of cabin units in Curry Village where many of the incidents have taken place. Curry Village took a hit when flooding in 1997 destroyed dozens of cabins, and proposals to remove more from the base area of the cliff would decrease housing units even more.

It was a great teaching moment...except that only four of my students had looked at a newspaper this morning.

The Real Jurassic Parks: Where are the Dinosaurs?

A great many parks on the Colorado Plateau draw their scenery from Jurassic-aged sediments, and have been reviewed on a fair number of posts in the last month or two (see here for a listing). I haven't said much about the dinosaurs themselves because I was waiting to talk about the ultimate dinosaur park: Dinosaur National Monument (a most creative name, don't you think?)

The park draws its fame for an extraordinary bone bed that was discovered in 1909 by Earl Douglass. Although thousands of bones were quarried and sent to distant museums, there was enough foresight among the powers-that-were to preserve hundreds of bones in place where they could be viewed in situ by the public. By 1915, 80 acres around the quarry were set aside as a monument by President Woodrow Wilson. The park was expanded in 1938 to include the spectacular gorges of the Yampa and Green Rivers, an area of some 200,000 acres. The park was the setting of one of the seminal battles in the nascent environmental movement in the 1950's when an effort to construct a huge reservoir in Echo Park in the heart of the monument was turned back (some details here).

The source of most of the dinosaur fossils in the monument is the Morrison Formation, one of the most widespread sedimentary units in the western United States. It is exposed over a region extending from Canada to New Mexico and from the Great Plains to Arizona and Utah, forming a unique badlands topography in shades of purple, red, green and yellow. The rocks reveal a vast river floodplain system that was occasionally mantled with volcanic ash from eruptions of stratovolcanoes to the south and west. A shallow sea existed to the north.

Rivers are wonderful settings for the preservation of fossils. Animals are drawn, of course, to river (fluvial) environments, and occasional floods will trap many of them. As rivers meander back and forth across the plains, point bars (inside loop of a meander) become collection points for animal carcasses. They can be quickly buried and preserved in such situations (the bone bed at Dinosaur NM is an example of this). The muds of the floodplains likewise can be a tomb for mired animals. In other situations, the muds served as nesting grounds for some species, and nests, egg shells and juvenile dinosaurs are counted among of the significant finds in the Morrison.

A phenomenal number of fossils have been found in the Morrison Formation, including dozens of species of dinosaurs, as well as smaller reptiles, pterosaurs, crocodiles, primitive mammals, fish, amphibians, and invertebrates. Many of the most best-known dinosaurs were discovered in the formation: stegosaurs, sauropods ("long-necks" to you parents out there), and allosaurs. Twelve species have been discovered in Dinosaur National Monument alone, including the Camarasaurus in the third photo above.

The clay-rich nature of the Morrison Formation has been the undoing of the most famous aspect of the park. The bone bed was exposed in a steep face that came to be protected under a three-story-high shelter. Over the years the soils have settled and the structure was seriously compromised, with cracks and fissures in the building that represented a danger to the staff and public. As a result, the building has been closed since 2006. Unfortunately, park visitation plummeted, and the budget situation at the park has deteriorated.

Because of the budget shortfalls, some political controversies have arisen in recent months over the management of Dinosaur National Monument and the role of paleontologists in the work force at the park. Rebecca at Dinochick Blogs has been on top of the issue, with the most recent flurry of letters here.

If you have the opportunity to visit the park, do not miss the 200,000 acres of the park that are not the fossil exposures! A vast plunging anticline dominates the park, and the two rivers that cross the anticline have carved deep gorges that are extremely popular with river rafters. A road climbs from the south boundary of the park to spectacular overlooks at Harpers Corner and above Echo Park.

Geologic Haiku

Tropical limestone ledges
High on Sierra peaks
A long journey completed

A new geology meme! Rules here. The picture is of Boyden Cave Roof Pendant deep in Kings Canyon in California's Sierra Nevada.