Colorado Plateau Trip (Sunset Crater)

Reading all of the current anniversary posts on Mount St. Helens in the geoblogosphere has reminded me that I should write about my trip throughout parts of the Colorado Plateau.  The trip lasted for nine days (May 9-17) and focused mainly on Utah.  Our guide for the trip and the teacher of our Geology of the Colorado Plateau class was Dr. L, he was insistent that our trip was merely a "sampling" of the geologic area and after spending eight days in the region I think I now understand what he meant.

We began our trip with a 7 AM departure time, agreeing beforehand that we would stick to "New Mexico" (Mountain) time throughout the trip to avoid confusion when traveling through Arizona.  We drove solidly through New Mexico, stopping only in Gallup for lunch before continuing on to our first national monument.  Throughout the drive it was interesting to note that the graduate students who made up the majority of our car were fascinated by the young, scattered volcanic features of Central and Western New Mexico.  They were thrilled by a paleovalley that had been filled by a basaltic flow and the cinder cones along the roads we took were often pointed out, even from a distance.  It was an enlightening experience to see how spoiled the Southwest (and New Mexico in particular) had spoiled me for dynamic geologic histories compared to the graduate students in our company.

We drove onward until arriving at Sunset Crater National Park.  Here we saw our first and last exclusively igneous parts of the trip.  Sunset Crater is a young cinder cone just north of Flagstaff.  It is 340 meters (1,120 ft.) tall, and erupted between 1080 and 1150 AD according to paleomagnetic data.

I found this cinder cone interesting mainly for how colorful it is (due to the young scoria deposits that cloak the cinder cone) and the impact it had on indigenous life in the area.  It appears that the 2100 km² of ash that blanketed the area forced out the native people known as the Sinagua Indians.

The educational and cultural aspects I gained most from this park were more small and personal than the cinder cone and the volcanic field that produced it however.  While walking the short trail at the foot of Sunset Crater I learned about a fascinating feature of volcanic fields: hornitos.

Apparently, these small openings are eruptions within eruptions and are produced by upwelling within lava tubes.  What is significant about hornitos at Sunset Crater is that the natives who evacuated the area apparently placed corn and presumably other goods within the hornitos as a ritualistic gesture, and some of the impressions from the sacrifices were preserved in the lava and are on display at the visitor's center.

Beyond that, this young volcanic field (the San Francisco Volcanic Field) held another treasure.  San Francisco Mountain, an eroded stratovolcano, was within view of the park and is believed to represent an analog to Mount St. Helens, due to its significantly eroded, asymmetrical body.

We camped that night on cinders, within sight of Sunset Crater at a place called Bonito Campground.  A cold front moved in late that night, raining and hailing on us in between strong gusts of wind.  Not a very auspicious first night, but it certainly wasn't the worst we saw on the trip...