Another Scene from the Colorado Plateau, for a Special Day

Today's posting is a view of the San Juan Mountains from the campus of Fort Lewis College in Durango, Colorado. It is sort of a transition zone from the mostly horizontal Paleozoic and Mesozoic sediments of the Colorado Plateau to the Proterozoic metamorphic rocks and the early Cenozoic volcanic centers of this corner of the Rocky Mountain chain. The town itself is surrounded by cliffs and slopes developed in the Cretaceous Mancos Shale. Coal mining took place nearby during the previous century.

I just love the town of Durango. It has always been a pleasant respite from the heat of the desert on our summer field studies journeys. I would arrange for a grocery stop, giving the students a few minutes to wander about the town, getting t-shirts, and restocking their ice chests. I got to know the town even better when my son decided to pursue an Anthropology degree at Fort Lewis College.

The town occupies some glacial outwash plains along a river with one of the most poetic names of any I have ever known: the Rio de los Animas Perdidos, the River of Lost Souls. It flows out of the Rocky Mountains, joins with the San Juan River, and eventually merges with the Colorado.

Why the special day, and why Durango in today's post? My son met his fiancee at Fort Lewis College in Durango, and today they are getting married! So, postings were a little light this week for probably obvious reasons. I've been distracted....

Grand Canyon's North Rim - The Transept

How many places are there in the world where a 3,000 foot deep canyon with walls so steep that one cannot see the bottom from the rim is an afterthought? The Transept is one of those special places on the North Rim of the Grand Canyon. It lies west of the Bright Angel Lodge on the rim, and is a large tributary to Bright Angel Canyon. You can look down into the canyon from the Transept Trail, a short stroll between the campground and the resort, or you can get a particularly spectacular view by walking about two miles out the Widforss Trail. The Widforss circles the rim of the canyon, providing the view down the gorge seen in the picture above.

The prominent cliffs in the lower part of the canyon are the Mississippian aged Redwall Limestone. The cliffs are about 500 feet high. The overlying redbeds are the Pennsylvanian-Permian beds of the Supai Group and the Hermit Shale. They are delta and floodplain deposits eroded from the Ancestral Rocky Mountains which existed at the time to the northwest in Colorado.

I had the privilege of seeing one of the last free-flying California Condors back in the 1980's in the hills north of Santa Barbara. When the population dropped to about 28 individuals, they were all captured and they started raising captive birds. As more and more of them matured, and the total number slowly rose, they began releasing the birds in the wild in a number of widely isolated locations in California, and in their old range of Arizona. A small population inhabits the North Rim at times. At the time of my last visit, I wasn't aware of the presence of these grand birds. But I did see some monstrously huge turkey buzzards flying around and finally realized that NOBODY was identifying turkey buzzards with number tags. These were condors, in range of my camera! It was a neat moment, although I kept trying to get a picture without the number tag, but getting a picture of a Condor with the Grand Canyon as a backdrop was thrilling enough.

What Would a Martian Do? Where Would You Land on Earth?

If I were a Martian and had five spacecraft, where would I choose to put them on Earth in such a way as to learn as much as possible?



I would have to start with the oceans. They cover 70% of the surface, hiding any structures in the rock, and providing an opportunity for life to arise. One of the first choices I would make is a shallow marine landing in the equatorial regions. It seems to me that vast areas of molten ice (that's how they would see it) would be mysterious and perhaps even inhospitable. I would leave it to the Martians to design a device that could explore the mysterious waters. Would it sink and sit on the bottom, or would they think to give it the mobility to explore different depths?



How would Martians see the chance of life developing? They live on a cold, dry planet with liquid water a rare phenomenom. Would they pick a landscape on Earth that is most like theirs, in hope of finding life there? How about the Dry Valleys of Antarctica? It might not tell them the most about the planet, but would it confirm their pre-conceived notions about Earth and the similarities it shares with their planet?

Erosional processes on Earth are clearly different from those on Mars. If I were them, I would aim for one of the boring places, such as the Central Valley of California, or the Mississippi River basin to get samples of soils that develop in depositional basins in order to learn something of the current and immediate past climate. What would they make of soil horizons?

On the other hand, vast eroded areas of bedrock would present an intriguingly new landscape for a Martian. I would pick a deeply eroded, but flat terrain that reveals as much geological history as possible. With a good eroded anticline and a rover, one could work out a geological history for an area quite readily. I am thinking maybe some of the anticlines in Wyoming, or the Virgin Anticline near St. George Utah, or the Kettleman Hills in the Central Valley of California. Another erosional landscape would be one of the shield areas such as those found in parts of Australia's Outback, or northern Canada.

The Martians would surely be curious about active river systems and stream erosion. There would be obvious benefits in exploring a river gorge that exposes a great deal of geology, like the Grand Canyon, but I wonder about the technological challenges of exploring such a place with an un-manned (un-martianed) craft.

Finally, wouldn't they be drawn towards active volcanoes? They will have studied their own ancient shields, and understand the rock chemistry, but they never will have seen an erupting volcano. Would they shoot for the Big Island of Hawai'i, or Mt Etna? Or would our shield volcanoes seem too pedestrian? Would they go for a big stratovolcano instead? What about Cleveland or Augustine in the Aleutian Islands?

Martians Coming to Study Earth! Where Would You Land?

Congratulations to NASA for their successful landing on Mars! They are starting to beat the odds, as something like half of all landings have failed (I imagine the Martians shooting our spacecraft out of their atmosphere like an "Asteroids" game). Others in the geoblogosphere have discussed what we hope to find (here, here, and here), but I am curious:

If you were a Martian, and had five chances to land a spacecraft on Earth, what five locations would you pick to land in such a way as to learn as much about the planet as possible? Imagine that you have mapping spacecraft that provide high quality photographs of the surface, but that you know no more about Earth than we do about Mars.

I will give it some thought and offer my suggestions, but I haven't had time to think that far ahead.

Why I Love the North Rim

Seeing my students graduate is really great, but taking a person to a place like the Grand Canyon for the very first time is an even greater thrill for me as a teacher. We stay most years on the North Rim most years for a number of reasons.

The South Rim gets something like 90% of the visitation, which is reason enough to avoid it, but because more people are there, the rim has more trailheads, more facilities, museums and so on. The North Rim, in contrast, is around 1,000 feet higher, cooler, and more moist, and thus the forest is predominantly composed Ponderosa Pine (instead of pinon), and there are more meadows. One of the nicest aspects is the location of the group campground: it is only a few hundred feet from the rim (South Rim campgrounds are nearly a mile back). I prefer the views from the North Rim; the higher elevation offers a panorama of the landscape south of the rim, including the San Francisco Peaks volcanic field.

Today's picture is a morning shot looking south towards the San Francisco Peaks. I will have to leave it to others who know more about this kind of thing to explain why there is a gigantic composite volcano and associated volcanic field here. I imagine there is a sort of 'manhole' effect where lavas are leaking out from under the thick continental crust of the plateau country where it has been faulted by the current extensional regime, like a sewer system backing up. The high point on the rim, Humphrey's Peak is over 12,000 feet high (Arizona's highest mountain), but the original summit may have been several thousand feet higher. From the east, the complex looks surprisingly like Mt. St. Helens. The field is mostly Pleistocene, and at least one volcano erupted within the last 900 years (Sunset Peak National Monument).

Why I Teach - Spring 2008 Edition

Among all the other things going on this time of year, graduations are really special. I have had the privilege in the last two or three years to see my daughter, son, and wife graduate from college, and last month, my one-week-away-from-being-my-daughter-in-law too (see my other blog if you REALLY want the details!). But it is also really special when some of your students make the big transition, especially when the odds were long, and the situations were difficult. Yesterday I was in Sacramento to see one of my former students take the walk across the stage. It was a happy moment!

This is a geology blog, so I will point out that she graduated with a degree in geology. There is a grad school out there that will be lucky to have her in the program in a year or so, and later on, a company or school is going to have a very talented employee. Congratulations!

Faults and Folds Weekend Fotos!

Following the example of Silver Fox and Lost Geologist, I decided to throw a fault and fold foto into the geomix this weekend. This is also still on the theme of my impending Colorado Plateau journey, not because it is there on the plateau, but because this is often my first stop on our trip. It has it all for a first day geology student: faults, folds, stratigraphy, unconformities, paleontology, economic geology, and nearby archaeology. Geologists from southern California will recognize it right away as the Barstow Syncline, located within the Barstow Formation, and exposed in the appropriately named Rainbow Basin Natural Area. I did my very first field mapping here, back in 1979 or so, with Pomona College.

The syncline lies near exposures of the Calico fault, an active right-lateral strike slip fault. The Landers quake in 1991 ruptured part of the fault zone. A minor offset cuts the left limb of the syncline and other faults slice through the basin, making it an excellent place for mapping.

The layers exposed in the fold are terrestrial and fresh water sediments of the Miocene Barstow Formation, a critically important stratigraphic and paleontological element of southern California geology. The vertebrate fossils found here include early species of elephants, camels, antelope, three-toed horses, cats, and many others. In some nearby areas, silicified insects have been discovered as well. Because the layers of the formation are bracketed by dateable volcanic ash layers, they form the basis of the Barstovian Land Mammal Stage of the geological time scale. When similar species of animals are found in other parts of the country, they can be dated to around 15 million years by comparison to the Barstovian fauna.

Looking for a good example of an angular unconformity? Check out the layer of alluvium across the top of the fold! The region eroded to a relatively flat surface in Pleistocene time and was covered by alluvium, but more recently the land was warped upward and is presently being rapidly eroded.

The Barstow Formation was the host rock for barite and silver ores, as well as borate minerals, and a number of mining ghost towns dot the region. Calico is the most famous, and has been developed as a regional county park (read: tourist trap), but it is a nice enough place to visit. Kenny Rogers and the First Edition once actually produced a two disk record album full of songs about the ghost town. Farther to the east, the Calico Early Man Site offers evidence for the presence of humans in the western hemisphere far earlier than is accepted by most archaeologists.

Want to see Rainbow Basin? The Bureau of Land Management site offers the directions and information on camping and touring the region.

Update: It didn't take long to find out that others really love the place, too (and beat me to the blog post!). Ron Schott has a blog entry here (although I am having trouble following the link), and Dave Schumaker has one here. Thanks for the info!