A Tale of Two Arches, But Not in Arches

Travelers in the southwest might get the idea that arches can only be seen in Arches National Park in Utah. It's true that Arches National Park has the largest concentration of arches in the world, and the world's longest arch is found there, but arches have formed all over the Colorado Plateau. I saw two notable examples last week, and they can be seen in today's post.

Grand Staircase-Escalante National Monument has a rather spectacular version of one in Grosvenor Arch, about eight miles east of Kodachrome Basin State Park. The cliff is composed of Henrieville Sandstone (Jurassic in age), with a capstone of Dakota Sandstone from the Cretaceous Period.

It used to be called Butler Arch, but an expedition from the National Geographic came through the area in 1949, and they pulled strings to rename it after their boss. The biggest of the two arches is about 152 feet high, and 100 feet wide.

We heard an ungodly screeching all around us while at the arch, and it didn't take long to find the noisemaker: a bunch of cicadas. They look like horrifying beasts of Hades, but are essentially harmless.

Driving west from Grosvenor, we passed a nice viewpoint of Wiggler Wash, where the creek cuts through a fold, exposing the Entrada Sandstone and Henrieville Sandstone. The pink cliffs of the Aquarius Plateau can be seen in the far distance.

This was a tale of two arches, but I actually didn't mean the double arch of Grosvenor. The next morning we were at Bryce Canyon National Park, another place where arches form readily. One of them can be seen from a pullout in the southern part of the park. It's called Natural Bridge, but as the signs and irritated geologists will tell you, bridges span creeks, while arches form by other means. But it's pretty neat in any case.

My posting will be very spotty over the next two weeks. I had so much fun on my one week exploration of Grand Canyon, Bryce and Zion that I am headed back out there again, this time with two dozen students. We're making a huge loop through the plateau country, with no wi-fi motels, and rare access of any kind. I might actually have to breath the air, hike around for entertainment, and gaze at stars at night. I'll try to maintain a positive attitude!

The Cretaceous Parks of the Colorado Plateau: Walled Cities and Tragedy

A walled city of 400-500 people, surrounded by tilled fields, and constantly subject to attack during its short existence in the 13th century. A castle complex in England or France? No, it is one of the more intriguing sites on the Colorado Plateau that is almost unknown to the millions of tourists who pass through the region every year.

We have been working our way through the geological history of the Colorado Plateau, and in our most recent posts we have been reviewing the late Cretaceous sediments that formed along the margins of an inland sea that divided the North American continent into two. The Dakota Sandstone originated in the beaches of that sea, and forms an important capstone across the "fertile crescent" of southern Colorado and Utah. It is covered by the rich Dove Creek Soils that provided the Ancestral Pueblo people with corn, squash and beans (beans are still grown across the region today).

About 165,000 acres in the region are preserved as Canyons of the Ancients National Monument, which has to be one of the unique parks in the American West. Where most parks include campgrounds, carefully labeled overlooks and exhibits, various visitor services and efforts to attract tourists, Canyons of the Ancients has none of these things. If anything, the administrators of the park would just as soon discourage visitation. Why? Because the park was established to preserve one of the densest concentrations of archaeological resources in the country, and they have almost no resources with which to do the job. The park lacks the spectacular cliff dwellings that are so characteristic of Mesa Verde National Park, and most of the ruins lie beneath hills and mounds of rubble. And yet it is a treasure...

I have had only a few opportunities to explore the mysteries of Canyons of the Ancients, but I learned more in those few trips about life in the Southwest than pretty much all of my previous journeys in the region. With little prior background, I participated in a geo-archaeological field trip to the head of Sand Canyon in 2003. We first paid a visit to the Crow Canyon Archaeological Center, which has conducted many of the surveys of the ruins in the monument. Along with the Anasazi Heritage Center, it serves as source of information on the park.

We drove across the beanfields, and I quickly became aware that ancient villages were scattered everywhere across the mesa surface, including right in the middle of some of the modern pastures as sage-covered mounds that the farmer's plows avoided. When we reached the end of the road, we got out of our vehicles, and wandered through the pinon forest to the upper rim of Sand Canyon. It was a little tricky finding a pathway through the boulders and rocks that lay scattered across the surface. Still kind of ignorant, I had not stopped to think how boulders and rocks did not fit with the topography, which was composed primarily of fine-grained soils. It was at that moment that our trip leader pointed out that we had reached the center plaza of a huge Ancestral Pueblo village that once housed 400-500 people. Looking around, I realized that every single boulder and rock around me was once part of a wall or a kiva. Look at the two photos above. Hidden beneath a pinon forest, little evidence can be seen indicating the presence of a village.

It was an amazing complex. An eight-to-ten foot high masonry wall surrounded the entire city. Water for the hundreds of people was provided by a single spring that was fed by the groundwater from an area of only a few acres. The village contained some 420 rooms, 95 ceremonial kivas and 14 towers. And yet it was built and then abandoned within a period of only 30 or 50 years in the late 1200's. Things did not go well at the end; environmental degradation and drought had caused stressful conditions, and evidence found at the site suggested the population was an aggregation of several scattered smaller villages in the region, come together for defensive purposes. Researchers also found evidence that an attack may have brought an end to the existence of the village itself, with burning of buildings and unburied bodies, victims of a violent death.

I don't know that I ever could have had the patience to do the actual excavation work, but the science of archaeology has always fascinated me. In so many ways the methods and technology of archaeology parallel those used in historical geology and paleontology, but there is an emotional component to archaeology that doesn't exist in fossil work. We are working with the remains of our immediate ancestors. They lived lives different from ours, and yet there are enough clues to understand something of their beliefs and hopes and fears.

We drove back to our dorm at Fort Lewis College in Durango. It was an enlightening trip.

In the next post, a discussion of another site at Canyons of the Ancients, the Castle Rock Complex.

The Cretaceous Parks of the Colorado Plateau: The View is Nice but Access is a Problem...

Looking for a good fixer-upper in Utah/Colorado? Have I got a place for you! This is one of a continuing series on the geology of the Colorado Plateau. It's taking a lot longer than I thought it would, and I thank you for your patience if you are still following the story! For several months we have been making our way forward through geologic time via some of the most beautiful places on the planet. For the early Cretaceous, we took a brief foray into Montana for a 1994 dinosaur dig in a layer (the Cloverly Formation) that was a substitute for the very similar Cedar Mountain Formation of the Colorado Plateau.

The remaining Cretaceous layers of the Colorado Plateau reveal events that ultimately separated the North American continent into two parts, with a shallow sea that ran from Canada to Mexico. The fluctuating shoreline left a mixture of sands, silt and mud that accumulated to depths of several thousand feet. When the land was exposed, plants grew in profusion in the tropical conditions. Coastal lagoons and swamps produced a rock that would eventually be a two-edged sword to the inhabitants of the region: coal. The formations include the Dakota Sandstone, the Mancos Shale, and the Mesa Verde Group (which includes a number of- formations that go by several names in different parts of the plateau region).

The story began with the rise of a mountain range in far west California and Nevada…where the Sierra Nevada stands today, a series of volcanoes spewed ash and lava. Deep underground, the magma cooled slowly to form the granitic rocks that make up the mountains we know today in places like Yosemite and Sequoia National Parks. Intense compression of the crust east of the Sierras in Nevada and western Utah caused huge sheets of crust to slide over each other forming a second series of mountains that shed vast amounts of sediment across what is now the plateau country.

The Dakota Sandstone and related formations are found across the region, from Montana to Arizona, and well into the Great Plains. It is usually exposed as a yellowish sandstone with prominent crossbedding. It formed as sea level rose and spread a blanket of beach sands across the region. Dinosaurs wandered across these beaches, but left only footprints and practically nothing else. No one would mistake it for a grand scenery-maker like the Navajo Sandstone, but it is a significant part of two unique national monuments: Hovenweep and Canyons of the Ancients.

Neither park is known for its geology; they were established for the Ancestral Puebloan (Anasazi) ruins that are found there. But geology played an important part in the life of the people who lived there centuries ago. At Hovenweep, the only layers are the Dakota Sandstone and the underlying Morrison Formation. The Dakota forms a resistant caprock that is topped by rich soils. In places, canyons have been carved into the softer rock underneath. The best-known ruins surround the head of Little Ruins Canyon, at the park visitor center and campground complex.

People live with the resources they have in the regions in they inhabit, and one can appreciate the difficulties of life in this harsh environment. But, despite the cold winters and hot summers, the soils were in an ideal location for growing beans and corn; high enough above the desert to get sufficient moisture, but low enough to have a longer growing season. Hovenweep sits in the middle of a “fertile crescent” that extended from Utah’s Cedar Mesa to Mesa Verde in Colorado. Thousands of people once lived here, and the land supported their needs, but droughts or other factors caused them to abandon the region in the 1300’s.

However much we may idealize their existence, one cannot deny the artistry of their architecture. Their structures follow the boulders and are built so well that they have perched there for centuries. So much is not known about their choices; why on the rocks? Defense seems the most logical reason, but defense from whom? And why put a four-story tower inside a canyon, rather than on the rim, where you could use it as a lookout?

Hovenweep is one of those overlooked gems of the National Park System. If you ever visit Mesa Verde National Park or Natural Bridges National Monument, it isn't much farther to get to Hovenweep, and is well worth the effort. Many of the ruins remain unexcavated, and the feel is far more wild than the paved trails of Mesa Verde.

Canyons of the Ancients will be covered in the next post!

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!