Geobulletin alpha

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Date:	2016-04-10 00:05:47
Blog:	WATCH FOR ROCKS - Travels of a Sharp-Eyed Geologist
URL:	http://www.watchingforrocks.com/2016/04/living-dream-day-5-granite-gorge-and.html

Summary:

We huddle together, this early May day, on a 12–person (14, if you include the guides) inflatable J–rig party boat that glides through the rapids with relative ease. We are ready for whatever thrill these cold riffles and rapids offer, so we hold on less and less, jostling and bouncing our way down the Colorado River. Soon the canyon narrows. Its vertical walls become higher, with fewer escape routes should anyone need to climb out. The rapids become larger and longer. We are within the ancient metamorphic rocks of Granite Gorge, home to the deepest, darkest, oldest, and baddest rocks in Grand Canyon. These are the crystalline basement rocks that underlie the North American continent. I am exactly where I want to be. Into the jaws of Granite Gorge (click on any pic to enlargenate)However, it is no wonder that, back in the summer of 1869, John Wesley Powell’s men loathed and feared this stretch of the Colorado River. They had endured so much already. One of their boats, the No–Name, had been lost early on their exploratory expedition of the river and its canyons. One member had already turned back not far from their starting point at Green River, Wyoming. By the time they passed the Little Colorado and entered Granite Gorge, their meager rations were even more meager, lost to spoilage and the river. Their oak boats had been swamped in the rapids. They had lost oars. Their clothes were threadbare and shoes were a luxury. Where shoreline existed Powell and his men would use rope to “line” their boats down a particularly troublesome rapid. If lining was not possible they would portage, carrying every single item including their unwieldy boats across massive boulders. It could take all day.   Granite GorgeCrystalline basement rocks in Granite GorgeRegarding Granite Gorge, Powell would later write in his Report: “We are ready to start on our way down the Great Unknown. Our boats, tied to a common stake, are chafing each other, as they are tossed by the fretful river. They ride high and buoyant, for the loads are lighter than we could desire. We have but a month’s rations remaining. The flour has been resifted through the mosquito net sieve; the spoiled bacon has been dried, and the worst of it boiled; the few pounds of dried apples have been spread in the sun and reshrunken to their normal bulk; the sugar has all melted, and gone on its way down the river; but we have a large sack of coffee. The lighting of the boats has this advantage: they will ride the waves better, and we shall have but little to carry when we make a portage.   We are three quarters of a mile in the depths of the earth, and the great river shrinks into insignificance, as it dashes its angry waves against the walls and cliffs, that rise to the world above; they are but puny ripples, and we but pigmies, running up and down the sands, or lost among the boulders.     We have an unknown distance yet to run; an unknown river yet to explore. What falls there are, we know not; what rocks beset the channel, we know not; what walls rise over the river, we know not. Ah, well! We may conjecture many things. The men talk as cheerfully as ever; jests are bandied about freely this morning; but to me the cheer is somber and the jests are ghastly.” (quoted in “Beyond the 100th Meridian” by Wallace Stegner)   And unsuccessful attempt at air drying after running the rapidsIn Granite Gorge, Powell and his men had no choice. They had to run the rapids. The river, squeezed into the narrowest of channels, grabbed hold of their boats and would not let go. There was little to no shoreline for a camp site. They stopped when daylight ran out or they were exhausted, or both, and curled up to rest among the boulders and beneath the cliffs, the ceaseless roar of the river their constant companion. The monumental walls concealed the sky, and along with the waves and rapids took up all the space and left them with little of comfort.   Neoprened feet photoThe element of the unknown is vastly different now than it was back in 1869. We do not travel the same river as John Wesley Powell and his men did. Today, Glen Canyon dam controls the amount of water that flows downstream. Maps tell us what to expect at each river mile. We have it easy, with our neoprene booties, waterproof rain gear, soft sandy camp sites, and meals that include coffee with sugar and bacon that is not rancid. Safety is crucial.     Nevertheless, the excitement still exists, if not the fear. We embark on a journey down the Colorado River with our own set of expectations of the danger and hazards involved. Motorized J–rigs are some of the most stable craft out there, but there are other, smaller rafts and dories that ratchet up the thrill factor a few notches. I am here to appreciate the geology of Grand Canyon, the deep time of its rocks that are nearly two billion years old. I want to experience the whole canyon in the time allowed me. I am grateful to those who came before me and, risking their lives, charted my route. Outstanding example of foliation in the schist**********************************************************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., Ilg, B., Williams, M., Hawkins, D., Bowring, S., and Seaman, S., Paleoproterozoic Rocks of the Granite Gorges, in Beus, S. and Morales, M., eds., Grand Canyon Geology, 2nd edition, Oxford University Press Stegner, W., 1953, Beyond the Hundredth Meridian: John Wesley Powell and the Second Opening of the West, Penguin Books (1992) Stevens, L., 2013, The Colorado River in Grand Canyon – River Map & Guide, Grand Canyon Wildlands Council

Content analysis:

Geographic context:

Location	Country	Latitude	Longitude
Colorado	US	38.9979	-105.551
Colorado Plateau	US	36.7871	-110.481
Glen Canyon Dam	US	36.9348	-111.486
Grand Canyon National Park	US	36.2846	-112.808
Great River	US	40.7217	-73.1575
Green River	US	41.515	-109.47
Oxford	US	34.3612	-89.5289
Portage	US	41.5857	-87.1794
United States	US	37.1679	-95.845

Keywords:

Colorado River