Geobulletin alpha

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Date:	2017-04-02 00:43:00
Blog:	WATCH FOR ROCKS - Travels of a Sharp-Eyed Geologist
URL:	http://www.watchingforrocks.com/2017/04/living-dream-day-7-grand-day-in-grand.html

Summary:

Occasionally in this life, we find that some days are better than others. Now and then, though, they all happen to be extraordinary. If we are lucky enough, we find each day to be as wonderful as the last. We savor each moment, not knowing what is ahead but realizing that life is an adventure and that we are indeed fortunate to be alive in a particular place. That’s how it is with my river–running friend Kris and me, during a glorious early May, on our week–long raft trip down the Colorado River in Grand Canyon. Breaking camp (click on any pic to enlargenate) I don’t see how the trip can get much better than what we have seen so far. However, the day is young, and apparently there are more surprises waiting for us downstream. We load our gear and selves onto the rafts and shove off.   The next thing we know the guides have maneuvered the rigs end–to–end, and we are sitting sideways in the channel. At a mere 76 feet wide, this is the narrowest point of the river. I’ll bet if John Wesley Powell and his boys were sitting sideways in this stretch, they were definitely not doing so on purpose.     The river carries us along gently through Granite Narrows and the Vishnu Schist.   Vishnu Schist I wonder who lives in there... Somewhere along river mile 136, between the narrowest part of the river and Deer Creek Falls downstream, the tilted layers of the Bass Limestone (of Grand Canyon Supergroup fame) crop out at river level above the Vishnu Schist.   It's the correct river mile, for the Bass Limestone...hmmm...   We tie up and follow a short trail, scrambling over boulders to reach the 100–foot plunge of Deer Creek Falls. A peek at Deer Creek Falls The two river rats Downstream from Deer Creek the rocks change. We leave the Precambrian granites and schists for familiar sedimentary layers. Here, regional westward tilting of the rock layers of the Kaibab Plateau enables the thick cliff–forming Paleozoic limestones to crop out at river level. Around river mile 145, the Cambrian Muav Limestone appears. We stay within its walls for a good part of the day.   I'm thinking Muav Limestone... Those massive, towering cliffs above the Muav can only be the Mississippian Redwall Limestone. At river mile 144, Kanab Creek comes in on river right. I could get out of the boat right now and hike up this canyon all the way to Fredonia, AZ, and hitch a ride home. After a brief consideration of the likelihood of my survival choosing this choice, I choose to remain in the boat.   Kanab Creek According to my river map and guide, this is the Muav Limestone at river level.   After lunch, the guides pull up to a beachless bench of Muav Limestone, nimbly swing the rafts around so they face upstream, and tie up against the current. Here, Havasu Creek pours inconspicuously out of its side canyon, a tributary second only in size to the Little Colorado. Although the turquoise water might put someone in mind of a glacial lake, the color is due to microscopic particles of calcium carbonate dissolved from the limestones. Travertine deposits coat the gravels and boulders along the creek bed. Havasu Creek is one of those places at which the day could hardly get any better.     Along a serene stretch of river I put my camera away and let my eyes and mind wander. For the next 15 or so river miles there are few rapids. We glide gently along, the motors of our rafts humming quietly as the canyon walls softly echo our thoughts.   We tie up for the night at Stairway Canyon beneath a sloping Bright Angel Shale. Our guides make it a point every day to stop and camp by late afternoon, giving everyone plenty of time to set up their tents and enjoy the evening Happy Hour. Evening slowly blurs into night, headlamps are lit, and the stars come out twinkling.   Home sweet tent View from the loo Looking west into the late afternoon ************************************************************************************* References:   Abbott, L., and Cook, T., 2004, Hiking the Grand Canyon’s Geology, The Mountaineer Books 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 Karlstrom, K.E., Ilg, B.R., Williams, M.L., Hawkins, D.P., Bowring, S.A., and Seaman, S.J., 2003, Paleoproterozoic Rocks of the Granite Gorges, in Beus, S. and Morales, M., eds., Grand Canyon Geology, 2nd edition, Oxford University Press Potochnik, A.R., and Reynolds, S.J., 2003, Side Canyons of the Colorado River in Grand Canyon, in Beus, S. and Morales, M., eds., Grand Canyon Geology, 2nd edition, Oxford University Press Stevens, L., 2013, The Colorado River in Grand Canyon – River Map & Guide, Grand Canyon Wildlands Council

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Colorado River