The only geologist on an archeology trip

Way back in graduate school my emphasis was on the glacial history of the Colorado Rocky Mountains. At the time, I loved the alpine environments, the cold temperatures and the climbing associated with glaciers. However, as I have grown older I have found that I enjoy the warmer climate of the desert southwest. Please don't get me wrong, I still spend time in an alpine environment, but the desert places have captured a big part of me.

While exploring the canyons found in the southwest I have changed my geology interests from glacial episodes of the Quaternary to the ergs of the Mesozoic. With more and more time spent in the canyons, I have found a strong interest in the previous occupants of the canyon country. You can only look through so many ruins and see so many rock art panels before you are just driven to know more.

So, a few weeks ago I joined a group of both professional and amateur archaeologists on a float down the San Juan river in SE Utah. What fun! What great examples of rock art. And, I was able to explain how some of the geology happened to be. The story in the rocks actually started 350 million years ago...not just 1100 years ago

Chert nodules

iron concretions. Many of my fellow explorers were not ready for a little chemistry lesson at river side to explain the origin of either the chert or the concretions.
The rock art was tremendous

The Mexican Hat. What a great example of the more resistant cap rock
The Raplee anticline

Where did the Wingate go?

If you have read this blog for any amount of time, you have already gathered that my favorite formation on the Colorado Plateau is the Wingate sandstone. In fact, the cover photo of the blog is of the Wingate sandstone along the Green River. It is a late Triassic- Jurassic aeolian sandstone. The grains are very uniformed in size making fantastic conchoidal fractures when blocks fall from the cliff face. Making a very nice cap rock on top of the Wingate is the Kayenta formation. The Kayenta, an early Jurassic siltstone-sandstone showing evidence of mid energy stream action is cemented very well and acts as an excellent cap rock. The top most component of this group (the Glen Canyon Group) is the Navajo Sandstone. This sandstone is another Jurassic aeolian sandstone that hints at being one of the largest sand islands ever seen on planet earth.

But...back to the missing Wingate.

Most of my play area is in Southeast Utah along the Colorado and Green Rivers. This past month we have spent some serious time in South central Utah in the Paria drainage. Here we see the familiar Glen Canyon Group wit the navajo sandstone along the horizon, the Kayenta formation directly below but instead of another aeolian sandstone there the Moenave Formation with reddish siltstone and pinkish sandstone showing clear evidence of water deposition. What a difference from the windblown Wingate.

The story in the rocks suggests that perhaps, in the early Jurassic we would have been in a desert resort area with ponds and streams with a large desert just to the east. A paleo-Palm Springs?

Canyon cliffs of Navajo sandstone with the Kayenta formation making the canyon bottom

Canyon walls of Wingate sandstone
And 100 miles to the west... the high white cliffs of Navajo sandstone, the reddish ledges of the Kayenta formation and the reddish-pink slope forming Moenave formation near the bottom.

high water

Last weekend while exploring different parts of the Uncompahgre Plateau we came across an unfortunate place to leave a truck. With the recent warm weather (and the extra long cool spring) the rivers are coming up high and fast.

Its not only the rafters that need to be careful around rivers.