|Putting in at Lee's Ferry|
(click on any pic to enlargenate)
|Putting in at Lee's Ferry|
|Kris is all smiles as we start our adventure|
|View from the front of the raft|
|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.
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|
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