Friday, May 6, 2011
I didn't know we were going in search of cross bedding the day we decided to circumvent downtown Zion Canyon (a place you can get to via shuttle, a Red Pass, by bicycle, or on foot), to take the side road under and over the mountain: the Zion–Mount Carmel Highway. I remembered from long ago, and indeed the Zion Canyon Map confirmed, that an overlook trail takes off back towards the canyon just past the main tunnel, a tunnel that is 1.1 miles long and was built in 1930 (Google Maps Street View of the tunnel near the first window). I had very little memory of the trail, other than that it provided an overlook of the lower part of Zion Canyon.
The trail is entirely in (or on) the Jurassic Navajo Sandstone, a thick dune sand recognizable in cliffs from miles away. I smiled the entire length of the trail and back: I think it was the cross-bedding. The hike may have stirred some sentimental sentiments (about these cross-bedded sediments), but if so, the stirred memories are buried too deep to make a difference to me today.
The trail is a 1 mile round trip with a total change in elevation of 163 feet. It's rated as moderate, mostly because of some narrow passageways and long drop-offs. Handrails are provided in particularly steep parts and where drop-offs are particularly dangerous or where the trail is narrow or slippery. At least one person has died after falling 400 feet from the end-of-trail overlook.
The trail begins in a set of steep stairs carved into a pale orange part of the Navajo.
Views are everywhere stunning. A leaning tree frames the fore trail.
Looking back under the leaning tree provides a view of the ever-present cross bedding.
A somewhat narrow part of the trail has a small seep near the base of a sandstone cliff.
Cross bedding! The trail, hidden by trees at the base of the cliff, goes on beyond a little embayment in the canyon.
More cross bedding, a little below the previous shot. Rocks are perched in a manganese-stained gully.
The trail — becoming a boardwalk hung over a hundred to two hundred feet of air — is about to enter a small alcove or cave.
Water seeps all along the base of the overhang, drips down the back wall, and drips from the ceiling. The air was already cool before we entered the cave, possibly not quite 70° F; inside the cave it was cooler and damper, probably a great place to hang out in the heat of summer. For scale, you can see footprints in the foreground on the sandy floor; the height near the farthest shade-sun boundary (with tree to the left and rocks to the right) is about 12 feet.
An inset arch can be seen from the cave, across a slot-canyon portion of Pine Creek.
The trail is still hidden by trees.
Now we're walking along a narrow ledge cut in sandstone, just above this Indian paintbrush.
Looking back toward the trailhead and the bridge coming out of the mile-long tunnel, we can see the slot-canyon portion of Pine Creek. MOH said he could see the bottom of the canyon with binocs. The rocks on the bare sandstone in the lower part of this photo are the same rocks perched on cross beds from six shots back (second of two cross bedding photos before the cave).
The rocks will someday plunge into the slot canyon below.
While taking a little side trail, we came upon a small herd of six to ten Bighorn Sheep, ewes with at least two lambs.
A lamb amongst the cross beds.
After a little less than an hour of moseying along, we arrived at our destination, the canyon overlook above The Great Arch (MSRMaps location, Google Maps photo).
NOTE: This post is part of a slow-to-develop geoblogospheric meme: Sentimental Sediments, started bravely by Dana over at En Tequila Es Verdad. Entries are supposed to be about your favorite sedimentary rock or sedimentary structure. As a hard rocker, I had a hard time thinking of any particular sed rock I'm actually sentimental about, but the whole of red rock and canyon country in the southwest contains my favorite sedimentary rocks and favorite stratigraphy, with any sentimentality on my part dating back to 1971 or 1973. At first I didn't think I had any digital photos from the area, but I have some from Fisher Towers and the San Rafael Swell. Now I also have some from Zion. :)
The entire geoblogosphere has been tagged!
Loope, D.B., and C.M. Rowe, 2005, Seasonal Patterns of wind and rain recorded by the Navajo Sandstone: Canyon Legacy, vol. 54, p. 8-12.
Loope, D., L. Eisenberg, and E. Waiss, 2004, Navajo sand sea of near-equatorial Pangea: Tropical westerlies, slumps, and giant stromatolites, in E.P. Nelson and E.A. Erslev, eds., Field Trips in the Southern Rocky Mountains, USA: Geological Society of America Field Guide 5, p. 1-13.
Loope, D.B., M.B. Steiner, C.M. Rowe, and N. Lancaster, 2004, Tropical westerlies over Pangean sand seas: Sedimentology, vol. 51, p. 315-322.
Stewart, Michael, 2006, Zion National Park: University of Illinois, Geology 104, Geology of National Parks and Monuments, Course Lecture Material (web only).