Monday, November 2, 2015

Living the Dream, Day 2 – Goodbye Moenkopi, Hello Coconino

We are up at 5am in the northern Arizona spring dawn, knocking back styro-cups of bad hotel room coffee and microwavedly weak tea. Kris takes off out the door for a pre-float jog. I stand in the middle of the room, bewildered, alternately stuffing stuff into or pulling stuff out of my dry bags (How many field guides do I really need?). Binoculars could come in handy, though, so back in they go (Damn, those little rascals are heavy). Kris returns refreshed. We eventually manage to drag our bags down the hall, into the elevator, and out into the lobby by the appointed 6am time, along with 21 other people of our ilk who have gone through pretty much the same ordeal. Kris stores her remaining valuables in a storage room locked until our return. I throw all leftover field guides into the back of my car and lock it, hoping it will be there when I return. After checking out of our rooms we are herded, along with 69 dry bags of assorted weightiness, into the latest reincarnation of an old school bus, upon whose seats we are soon swaying seatbelt-free and gleeful along a downtown stretch of Route 66.  We turn north onto highway 89 and are on our way out of Flagstaff toward Lee’s Ferry, our put-in point.
Putting in at Lee's Ferry
(click on any pic to enlargenate)
Our four river guides are already there, having come the previous night and loaded the two rafts with enough provisions to keep everyone comfortable for the next eight days. I find out later that everything on the raft has its place.  Our seat mattresses are also our sleeping pads. Each menu is packed in order of which day it would be served, in order to minimize the coolers being open. In the chill of early May having the coolers open might not be such an issue, but in the melting heat of mid-summer it could be critical, especially if you want ice with your evening cocktail. Oh, yeah.


Putting in at Lee's Ferry
We form bucket brigades to load the rest of the gear, drop our beer into mesh bags which will drag in the river alongside the raft, and listen to at least one more safety advisory (Keep your life jacket on! Don’t wear flip flops like the guides do!). We all hop on board as gracefully as age will allow. The guides shove our J-rigs away from shore and point them in the direction we want to go.


Kris is all smiles as we start our adventure
We embark upon our geologic journey within the 245-million-year-old redbeds of the Early Triassic Moenkopi Formation, with its familiar “bacon stripe” layering as seen near Zion National Park. We are on the Colorado Plateau, where Paleozoic and Mesozoic sedimentary rocks have undergone little deformation since they were deposited starting 570 million years ago. A fold here, a fold there, but basically every layer is flat-lying in relation to those layers in contact above and below it. There are older rocks, however, that have their own tilted configuration, the Grand Canyon Supergroup of tilted Precambrian sedimentary rocks that are between 1.2 billion and 800 million years old, but they are days away. These outcrop only in very limited areas along the river, too, and so I hope the guides will point them out. For that matter, I hope the guides point out everything!


View from the front of the raft
The river will take us “down section,’ from younger to older rocks, from flat-lying sedimentary layers into the swirls and whirls of metamorphic rocks in Granite Gorge. Again, those rocks are days away. For now, sedimentary rocks are the name of the game. Our rigs bounce gently across the Paria Riffle, where the tops of Middle Permian cliffs of 260-million-year-old fossil-rich Kaibab limestones peek at us at river level. These cliffs, along with the lower and older Toroweap slope-forming rocks, record the advancing and retreating of a shallow sea over the ancient western continent. They disappear from view, though, above and beyond the older cliffs of Coconino Sandstone that begin to appear at river level.


Coming up to Navajo Bridges
Soon we pass beneath the cliffs Coconino Sandstone at the Navajo Bridges. It is a long way up to where Kris and I stood yesterday and gazed thoughtfully down at the river.


View from the front
We glide silently except for the occasional soft drone of the motor, which I can’t even hear unless I sit in the back. As the days pass, it becomes clear that there are “front of the boat” people and “back of the boat” people. I’ll bet you can guess which group I belong to from the get-go. I do take my turn in the back on occasion, though. The nice thing is that the back offers a sort of “bench seat” on top of a bunch of piled-up sleeping pads and so a gives view that skims the top of people’s heads instead of being blocked by the back of them. However, people in the back stay drier in the rapids than the folks in front, so I guess in the end everyone seems happy with their allotted space. When we come upon a rapid, though, everyone has to stay out of the way of the boatman with heads down, so he can steer us through without crashing onto any submerged rocks.

Incoming rapids!

Coconino Sandstone is Early Permian, around 275 million years old. It forms massive cliffs and is conspicuously cross-bedded, recording the movement across the arid landscape of a large Sahara Desert-like dune field that extended all the way to present-day Montana. As far as I can tell from my limited research, no body fossils (bones) have been found in the Coconino. These were pre-dinosaur days, and it is the tracks of small animals that are given a scientific name, not the animal itself. Vertebrate and invertebrate trace fossils (those sedimentary structures consisting of a fossilized burrow, track, trail, bore, or tunnel that resulted from the life activity of some animal) seem to be the only evidence that any organisms ever passed across these ancient dunes.

Researchers have carried out many experiments that compare fossil traces and those formed by modern organisms such as scorpions. With these smaller critters, it was dry sand that maintained an impression; they were unable to make any impression in moist, wet, or saturated sand. Larger modern critters such as lizards were able to leave tracks in wet or damp sand, though. It is thought, however, that the mists and fog of a coastal sand dune environment would have provided enough moisture to dampen and so preserve a track that had already been formed. Interestingly, the potential for track preservation in dry sand is thought by some researchers to be greater if the critter moved horizontally across the sand or up a dune slip face rather than down. On the other hand, if the sand was damp then a downslope-directed track was more likely to be preserved.

Coconino Sandstone cliffs overly slope-forming Hermit Shale

We continue down section on this afternoon of our first day, trying to absorb the grandeur of it all. Soon we bid farewell to the Coconino Sandstone at river level. The Hermit Shale awaits our curiosity, around the next bend in the river.

Hermit Shale at river level



References:
Blakey, R. and Ranney, W., 2008, Ancient Landscapes of the Colorado Plateau, Grand Canyon Association
Collier, M., 1980, An Introduction to Grand Canyon Geology, Grand Canyon Natural History Association
Middleton, L., Elliott, D., and Morales, M., 2003, Coconino Sandstone in Grand Canyon Geology, 2nd edition, Beus, S. and Morales, M., eds., Oxford University Press
Stevens, L., 2013, The Colorado River in Grand Canyon – River Map & Guide, Grand Canyon Wildlands Council

2 comments:

  1. Oh how I want to do the upper river.

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    1. It wouldn't hurt my feelings at all if I did ANY part of the river again! Just reviewing my pictures to include in the posts sends me into a swoon!

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