Headed into the Back of Beyond (Again)

I had hoped to finish our blog journey through the most dangerous plate boundary, but there was just too little time between real-world trips. The next journey is taking me and nearly two dozen students on a trip through time, both geological and anthropological. Our combined geology and archaeology class is exploring the fascinating landscapes of the Ancestral Pueblo people and other groups of the southwestern United States.

Archaeologists learning geology, and geologists learning archaeology. It's a symbiotic educational relationship that enriches students of both disciplines. We've done this trip a number of times, and it seems to get better every time.

This summer equinox picture of Fajada Butte at Chaco Canyon is emblematic of our trip, as we see Cretaceous sedimentary rocks of the Mesa Verde Group making up the cliffs and slopes. In the foreground, a small ruin from the people who lived on this land for more than a thousand years as a distinct culture. They then abandoned the region and 700 years later, a different group of people started to build roads again, with an asphaltic covering material (and mechanical air conditioning in their dwellings).

And all of the students are willing to dabble a bit in biology as well, especially when the object of their attention is so colorful.

Geotripper is going to be hit and miss for the next few weeks. I look forward to sharing our adventures in a few weeks!

The Abandoned Lands...A Journey Through the Colorado Plateau: Kasha Katuwe Tent Rocks, Erosion in Action

What happens when you take an arid landscape with faulting and high relief, add in some loosely consolidated poorly sorted sedimentary and volcanic rocks, and add yearly monsoon flashfloods? You get the Kasha-Katuwe Tent Rocks, a national monument located in New Mexico on the Cochiti Pueblo at the western edge of the Rio Grande Rift. This was the location of yesterday's mini-quiz, as noted by Chas in the comments.

Yesterday's post was all about looking at erosion from the bottom as we walked through a slot canyon on our way to the upper part of the mesa. Today we take a look at the upper reaches, to see what happens when erosion eats away at slopes composed of random boulders and cobbles in a matrix of finer fragments. The results are fascinating to see...

First are the pedestal rocks. Two formations are exposed at Kasha-Katuwe, the Peralta tuff (6.5-7.0 million years), and the Cochiti formation (2-6 million years). The Peralta was produced by a series of explosive rhyolite ash eruptions from the vicinity of Jemez (Valles) Caldera. The Cochiti has a mixture of sand and gravel with larger boulders. As the boulders are exposed by erosion, they protect the softer rocks underneath from erosion, forming the pedestals.

 Our hike takes us through the narrows that we explored in yesterday's post...

...and we emerge into the upper canyon where some tall hoodoos can be seen high above. The trail starts climbing in earnest.

And then there is the really weird stuff...the "tent rocks". I think of a tent is being dome-shaped, but it starts becoming apparent that the tents in this case were more like the tepees of the Plains Indians. These originated as pedestal rocks, but the boulders have rolled off, leaving the softer rocks to erode into the bizarre cones.

There are dozens of these odd tent rocks in the upper canyon. World travelers note the similarity to the rocks of Cappadocia in Turkey. The origin of the rocks is quite similar. In the case of Kasha-Katuwe, no one is living inside the cones as some people do in Turkey. The park area has been historically utilized by the people of the Cochiti Pueblo for hunting and plant gathering. The park was established by the Bureau of Land Management in cooperation with the Pueblo.

The trail ends at a marvelous lookout that provides views of the Rio Grande Rift and the distant Sandia Mountains, as well as a view into the canyons below.

But mostly it's the "tents" that latch onto your attention. I couldn't stop staring at the odd and bizarre shapes. I headed down the trail. It was time to head to our camp outside Santa Fe, as we got ready to two pueblos whose histories went in opposite directions, Pecos and Taos.

For the reasons for my odd title for this series, check out http://geotripper.blogspot.com/2012/06/abandoned-landsa-journey-through.html

Geo-Picture a Day Week: Kasha-Katuwe Tent Rocks National Monument

Geo-picture-a-day week continues with Thursday's offering: little-known Kasha-Katuwe Tent Rocks National Monument in New Mexico's Rio Grande Rift. The odd spires are hoodoos, caused when some kind of boulder or capstone prevented the erosion of the much softer rock underneath. The softer rock in this case is ash and pumice fragments from an eruption of a vent in the Jemez Caldera area about 6-7 million years ago. It is a bizarre landscape that reminds some people of Cappadocia in Turkey, which isn't surprising because the geological history is similar.

Kasha-Katuwe Tent Rocks National Monument is administered by federal Bureau of Land Management instead of the National Park Service. It is a fascinating place to walk around!

Time Almost Beyond Imagining: Who Do the Magic that Hoodoo?

Sorry for the title. Sometimes such things are irresistable, and geology terms sometimes seem to lend themselves to parody: subduction, orogeny, bedrock, schist and gneiss. Just the same, today's post is about one of the stranger places in the Colorado Plateau country: Kasha-Katuwe Tent Rocks National Monument on the flanks of the Valles Caldera, site of the previous post on the latest part of the geological story of the Colorado Plateau. It's got a lot of unique scenery packed in a small area.

The Valles Caldera is one of the nation's active supervolcanoes, and over a period of more than six million years, the eruptions of the center have blanketed the region with rhyolite tuff and ash. If you look at a physiographic map of the caldera you can see that erosion has sliced into the flanks of the volcanic complex, exposing evidence of older eruptions. The scenery at Kasha-Katuwe is the result of this geologically recent erosion of the soft volcanic rocks.

Some of the layers on the flanks of the caldera contain river and mudflow deposits with boulders and cobbles of all sizes. The larger boulders protect the softer underlying rocks from erosion until the boulders stand at the top of tall pillars (see the third picture). These are hoodoos. Eventually the boulders topple, and erosion attacks the underlying rock, producing the strange conical spires that give the monument it's name (the English part anyway; Kasha-Katuwe refers to "white cliffs" in the Keresan tongue). The erosion of the soft rock by flash floods in this arid environment have also led to the formation narrow steep-walled slot canyons (the fourth photo).

The monument is a bit tricky to find; the park brochure and location map can be found here. The New Mexico Bureau of Geology and Mineral Resources has a nice review of the geology of the region. If you ever pass through the Sante Fe-Albuquerque region on a field trip, check it out!