Sunday, April 15, 2012

Exploring The Canyonlands in Utah - Part 1

Last week I was up in the Canyonlands area near Moab, Utah leading a small group of enthusiasts with the Museum of Northern Arizona Ventures Program. We had an excellent time with all of us being veteran geology buffs excited to see the world-class stratigraphy that this area affords. One of my participants, Kent Colbath, is a great supporter and volunteer at the Museum and came along with his camera on the excursion. Long time blog readers of Earthly Musings will be familiar with my photography here, but this time I thought it might be fun to see how one of my participants viewed the places visited on our five day trip. I will do this in a few different blog postings and here are the first two days of our trip. Have a look at what we saw and learned about.

Our first stop on the way to Moab was Monument Valley. Here we took a 3.6 mile hike around Mitten Rock, seen on the left. Monuments here are capped (top to bottom) by thin outcrops of the Triassic Shinarump Conglomerate and Moenkopi Formation. The major part of the cliff is composed of Permian  De Chelly Sandstone with lower aprons of the Organ Rock Formation. This sequence would be observed many times during our week in Canyonlands. The floor of Monument Valley and not visible here is the Cedar Mesa Sandstone.

After passing through Mexican Hat, Utah, we saw the Raplee Anticline where the Pennsylvanian Halgaito Shale (top red) and Honaker Trail Formation (lower red and gray) create a kaleidoscope of color along the San Juan River.

Our first day on the ground took us to Island in the Sky in Canyonlands National Park. Here is a NASA image of Upheaval Dome, an odd structure located atop the plateau. If you look very closely in the upper left, you will see the paved road that crosses the upturned Navajo Sandstone ridge and enters one of the inner rings of the structure.

Our first stop on the ground was Whale Rock, seen in the foreground. Here you can see a semi-circular outcrop pattern within the Navajo Sandstone. This is the outer ring of Upheaval Dome. Studies in the last 15 years have shown pretty good evidence that this is the result of an impact crater from a meteorite that hit the earth in higher (now eroded) rocks back in the Cretaceous Period (about 90 Ma). Another popular theory that is now mostly discredited is that the dome formed from the movement of underground salt. While on Whale Rock, I showed our small group a series of three NPS pamphlets that explain the formation of this structure. The first one was from 1983 and highlighted the salt some theory with only one sentence at the end dedicated to the impact theory. The second pamphlet was from 1991 and contrasted the two theories equally within it. The last pamphlet is from 2009 and the impact theory was given the vast majority of space in it. Inadvertently, I have assembled a crude history of thought on Upheaval Dome!
 
We hiked about a mile to two overlooks that allowed us to peer into the core of Upheaval Dome. What a mess! The impactor likely hit rocks that were about 4,000 higher than this. Subsequent erosion has removed the overlying material.

Beautiful Indian paintbrush on the trail near Upheaval Dome

Later in the day we hiked out to Grandview Point, the southernmost projection of the Island in the Sky. On the way back, Kent took our picture with the La Sal Mountain laccolith in the distance. See two of my previous blogs on lacccoliths here and here.


With a positive thinking group, we drove down the Shafer Trail off the rim of plateau. This old uranium haul road was a thrill and a half! Our van made it too.

Our van on the lip of the Shafer Limestone. This is near the place where Thelma and Louise drove off of the "Grand Canyon" in the famous 1991 movie.

Here I am pointing out the geology at the end of a fantastic day of geologic touring!

2 comments:

Gaelyn said...

Someday I'll go on one of your trips.

Wayne Ranney said...

Gaelyn - please do come along on one! WR