Saturday, October 17, 2015

New Mexico's Chama River - A Geologic Gem!

Note to the readers of Earthly-Musings:  I apologize for a seeming lack of postings in the last month but I have been busy with trips and numerous weddings. Stay tuned - an Australia and New Zealand adventure with Smithsonian Journeys will begin next week with many postings from down under.

For some, New Mexico may be the one Four Corner state least likely to be associated with the Colorado Plateau. This is not for a lack of colorful sedimentary rocks so much as its lack of famous national parks that might highlight its subtle charms. There is no Grand Canyon or Petrified Forest, no Zion, Bryce, or Canyonlands, and no Black Canyon of the Gunnison, Mesa Verde or Dinosaur National Monument. Only the isolated and southern Carlsbad Caverns come to mind when thinking about parks in New Mexico. But recently, some friends and I explored the officially designated Wild and Scenic Chama River  in northern New Mexico found northwest of Santa Fe. It is a hidden geologic gem!

The river is located just east of the Continental Divide and is tributary to the Rio Grande. The Chama was dammed in the 1930's to regulate its seasonal fluctuations for farmers downstream. I found it curious that one of the dams buttress walls was constructed within the Cretaceous Mancos Shale.

The El Vado reservoir is a high elevation recreation area with water added to the system from the San Juan River on the other side of the divide. A pumping system brings New Mexico their share of their Colorado River allotment. We were floating on San Juan River water but east of the divide.

 Stratigraphic column for the Chama River rocks taken from the BLM guide to the Chama River

After leaving the put-in, the rock strata show an obvious down-dip in the upstream direction. Thus we were getting into older strata as we moved downstream. Here, sandstone in the Morrison Formation  was at the surface.

Downstream view of the river from our first camp

None the tarp - we experienced some significant rain on the front end of this river trip but it did nothing to dampen our spirits for the extraordinary scenery we saw and warm comraderie of opur small group of eight.

The BLM  manages the river and has built some very nice sandstone approaches into the campsites. The ranger on duty at the put-in apologized for the "intrusion" into the wilderness but I thought they were well done and did not detract anything from the  experience.

A large boulder of Morrison sandstone attracts kayakers

Fall colors had begun in some box elder trees, even though this trip was over the Labor Day weekend

Beneath the Morrison Formation was the Todilto Formation, a gypsum rich deposit

This unit is commonly seen in northern New Mexico and was deposited along the arid shores of a shallow Jurassic sea.

As the rocks continued to rise up from the river channel, the next unit was the Jurassic Entrada Sandstone, the "star" of the Chama River corridor.

Our second night's camp was across from a beautiful cliff of red sandstone with conifers growing on it. This was great spot to watch the big rain that came later in the afternoon.

Tafoni in the Entrada Sandstone, fired from case-hardening of the sandstone.

Camp scene on the Chama River. From here we hiked up the cliff behind the camp.

And began to get a great view of the river canyon

One usually doesn't associate a red rock canyon with lush conifers but the Chama is a located in a special place next to higher country that draws in the precip.

What a place!

Telephoto view of the Chama River Canyon

Wide angle view downstream in the Chama River Canyon. The rain began shortly after this photo was taken.

A very foggy third morning greeted us after a night of rain and dampness

John paddles down into the receding cloud cover - the storm had passed

Bill and Don share a quiet moment on the river. Most of the "bigger" rapids on the Chama are located in the final stretch of the river trip. They are really fun Class II and III rapids.

More floating through the Ponderosa pines

The Todilto Formation caps th colorful cliffs of Entrada Sandstone at the southern end of the river canyon. The lower tree-covered slopes are part of the emerging Chinle Formation. In other words, there is no Glen Canyon Group in northwestern New Mexico.

A Benadictine monastery, Christ of the Desert, is located at the southern end of the river canyon and is connected to the outside world by a 15 mile dirt road. Check out the link I have provided to find out more.

Happy boaters! Many times during this three day trip, I reflected on how lucky I am to have such wonderful friends - all who own the proper gear and experience - that places us in such spectacular settings, doing wild and grand adventures!

Our last lunch was beneath an overhang in the Shinarump Member of the Chinle Formation

View upstream from the overhang

Alcove forming at the contact with the Entrada Sandstone and the shale within the Chinle Formation. These alcoves are common where aquifer rocks sit on top of an aquitard or aquiclude. The groundwater (before any canyon cutting) is "ponded" on top of the shale, thus weakening the cement in the overlying sandstone, such that when it is finally exposed, it weathers away faster.

Near the Gallina River coming in from the west

The lowest unit encountered on the trip is the Shinarump Member of the Chinle Formation, a coarse sandstone and pebble conglomerate deposited in a braided stream environment some 225 Ma.

Close-up of the Shinarump cliff near the Big Eddy take-out. This was a fantastic trip in a wonderful area. The Chama River charms and enchants!

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