John Wesley Powell, Canyon Geologist

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Image Dimensions: 1920 x 1080

Date Taken:

Length: 00:20:36

Location Taken: Colorado River, US

Video Credits

 

In cooperation with Grand Canyon National Park. Director: Edwin McKee, Producer: Walt Roeder, Script Writer: Carol S. Breed, Photographer: Tad Nichols, Photo Narration, Special Photography, and Film Editing: John Running, Sound and Effects: Don Hart, Voice of Powell: Henry Alcott, Narrator: Ed Brady, Artwork: Miriam Wiser, Powell Expedition Song, "Flow Gently Sweet Afton" written by Robert Burns (1791), played and sung by: Robert Sutton.
 

Transcript

It is 1869. Deep in the gorge of the Colorado River. Nine brave men approached the most dangerous part of their voyage. Theirs is the first expedition through Grand Canyon. It will be accomplished by a crew of untaught frontiersman and their leader, a one-armed Civil War veteran. Listen to the words of Major John Wesley Powell: “We are now ready to start on our way down the great unknown. We have but a month’s rations remaining. We are three-quarters of a mile in the depths of the earth and the great river shrinks into insignificance as it dashes its waves against the cliffs that rise to the world above. We have an unknown distance yet to run, an unknown river to explore.

“Flow gently, sweet Afton, among thy green braes, 

Flow gently, I'll sing thee a song in thy praise;

My Mary's asleep by thy murmuring stream,

Flow gently, sweet Afton, disturb not her dream. How lofty, sweet Afton, thy neighboring hills

Far marked by the courses of clear winding rills, 

There daily I wander as morn rises high

My flocks and my Mary's sweet cot in my eye.”

Grand Canyon of the Colorado River, mysterious and uncharted, it was obscured by fable and rumor. No one knew for certain what lay in its depths. In 1869, the canyon region formed the last blank space on the map, from northern Utah to Arizona's boundary with Nevada. Then the Powell expedition entered the unknown territory and raced against starvation down a thousand miles of the wild river. “The object is to make collections in geology and natural history and to add a might to the sum of human knowledge. If we can record a few facts, and from them learn a lesson, we shall feel repaid for toiled privation and peril.” Major John Wesley Powell was a geologist. In the canyon he recognized scientific facts more wonderful than any legend. He brought back vital concepts of geology from this region that he named Grand Canyon. “Stand on the cliffs at the head of Marble Canyon and look off down the river over a stretch of country that steadily rises in the distance. Then see, meandering through it to the south, the gorge in which the river runs. You can scarcely resist the thought that the river burrows into it, for it is lost under the great inclined plateau.” Superstitious people told Powell that the river plunged underground into fissures that would swallow up his boats. Powell trusted the scientific principle that rivers cut their own channels. His geology was self-taught, but he staked his life on it. Now, here was evidence on a grand scale that rivers have enormous cutting power. Towering walls of rock, polished and scoured by muddy water, hug every curve of the river. It seems a paradox that such spectacular erosion happens here, in arid country. Cut off from the river, a man could die of thirst. Hear Powell's vivid description of the arid lands: “The land scaped everywhere away from the riveries of rock. Cliffs of rock. Tables of rock.  Plateaus of rock. Terraces of rock. Crags of rock. 10,000 strangely carved forms, rocks everywhere. Wherever water does flow in this high dry region, it cuts canyons. The geologic map shows the pattern formed when steep canyons are incised into nearly horizontal rocks that lie high above sea level. “For more than a thousand miles the Colorado has cut for itself a canyon. Where lateral streams joined, narrow valleys divided, into a series of canyons. Every lateral creek has cut a canyon. Every rill, born of a shower, has cut a canyon.” Running water wears away the land until only gentle slopes remain. Velocity is reduced, down-cutting ceases. This is the ideal limit to the erosive process. Powell called it base level of erosion. In the depths of Grand Canyon, the river sweeps westward. As it cuts deeply across the grain of rock, it exposes very ancient, base-level erosive surfaces. These surfaces are preserved as unconformable contacts between rocks of different ages. Powell drew a sketch of this double unconformity.  “These rocks are dipping and unconformable with the rocks that are spread over their upturned edges. While they may make but 800 feet of the wall, they have a geologic thickness of 12,000 feet. Set up a row of books aslant. It may be a few inches from the Shelf to the top of the line of books, but there may be several feet of books measured directly through the pages. So, these rocks are tilted like the books aslant on the shelf. The tilting shows that the region was uplifted. Then erosion attacked the tilted rocks and removed ten thousand feet from the top. So, the beveled top of this section where it meets the horizontal rocks of a much younger era stands for millions of years of Earth history. At the base of the tilted layer another, older unconformity, marks their contact with the crystalline rocks below. These are the roots of mountains that stood as mighty as the Alps a billion years ago. They too were base leveled by erosion. Long-vanished rivers cut away all but the roots of these mountains at a time when life had just begun. “We see a thousand feet of crystalline schists with dykes of greenstone and granite. Dame Nature kneaded this batter of dough very thoroughly. The walls are now more than a mile high. A thousand feet of this is up through granite crags. I climb up the granite and go over the rust colored sandstones and the greenish yellow shales, to the foot of the limestone wall. On top of this great bed are layers of bright red sandstone. Then above are buff and gray sandstones and limestones. The limestone weathers in columns and peaks and pinnacles. Curious forms of standing rocks are arranged all along the brink of the canyon wall. The rocks lie in horizontal layers. Some are soft, many very hard. The softer strata are washed out. The harder remain as shelves or as the stony pages of some great book. I climb so high that the men and the folks are lost in the depths below, and the dashing river is but a rippling brook. All about me are interesting geologic records. The book is open, and I can read as I run. But somehow I think of the nine-days rations and the bad river and the lessons of the rock are but dimly perceived.” Powell was still enthusiastic, but his men were not. They griped that the major was afflicted with geology to an alarming extent. Surely he was afflicted. His right arm had been amputated after the Battle of Shiloh. In spite of this disability, Powell had entered the canyon. Now no hardships would keep them from completing the job. “It rains. When the storm bursts, it comes down as a flood from the heavens. I find a thousand streams rolling down on every side, carrying with them red sand. All these unite in one great stream of red mud. Traveling as fast as I can, I soon reached the foot of the stream. Wave follows wave, and rolls along, and is swallowed up and still the floods come from above. I hasten to camp and tell the men there is a river coming down. We make 12 miles this morning, and then we come to monuments of lava standing in the river. The whole north side is covered with black basalt. And on the very brink of the canyon stands a cinder cone, an extinct volcano. Vast floods of lava have poured down here and streams of molten rock have run into the canyon. What a conflict of fire and water there must have been here. Just imagine a river of molten rock running into a river of melted snow. What a seeping and boiling of the waters. What clouds of steam roll into the heavens.” About a million years ago, flowing lavas roared down a side Canyon into the Colorado River. Four times the molten rock poured in and cooled until it had built a dam of basalt and gravel as high as Boulder Dam across the river. The Colorado was trapped. It rose behind the dam and after a while it formed a lake. Then the river cut a new channel through the dam and carried away all but patches of lava along the walls. Later, new lavas cascaded over the rim, and a small crater of cinders grew on top. Today, Vulcan’s Throne stands above the lava flows that cascade down to the remnants of the lava dam below. Here where the water runs over lava boulders, are some of the worst rapids on the Colorado River. But for Powell and his men, the hardest ordeals lay ahead.

“Flow gently, sweet Afton, among thy green braes, 

Flow gently, I'll sing thee a song in thy praise;

My Mary's asleep by thy murmuring stream,

Flow gently, sweet Afton, disturb not her dream.”

“Our rations are still spoiling. We have now only musty flour, a few dried apples, and coffee. We must make all haste possible. If we meet with more difficulties, we may be compelled to give up the expedition.” Discouraged, desperate, three of the men climbed out here at separation canyon. They were killed by Indians. The rest of the Powell expedition came safely through the canyon on August 29th, 1869. The one-armed major became a national Hero. With government support for his Survey, he returned to the canyon to map the unknown plateaus. The geological structure of the plateaus, through which the river runs, are shown by Powell's diagram. The elevated district traversed by Grand Canyon, is broken into a series of plateaus broken by a number of faults and folds. The plateaus are steps in a great stairway to the Kaibab plateau. The edge of each step marks the line of a fault, or a fold.  Kaibab means “mountain lying down.” You must not think of a mountain range as a line of peaks, but as a broad platform from which mountains have been carved by the waters. We speak of mountains forming clouds about their tops, but the clouds have formed the mountains. “Lift a region above sea level and the clouds gather and purl their storms against it. Carving out canyons and cliffs and mountains.” The same geologic processes are at work in Grand Canyon today. Softer rocks are washed away. Cliff walls crumble. So, the gorges widen as the river deepens its channel. But now did the Colorado River come to cut Grand Canyon across such high land and against the structural grain. Why did it not choose an easier course to the sea? From the evidence he saw, Powell concluded that the river was there first. It simply maintained its course as the land rose along great folds. He called it an antecedent River.  A memorial to Powell's adventure stands on the rim of Grand Canyon. A greater Memorial endures in the concepts he gave to the science of geology. The carving and shaping power of the agents of sub-aerial erosion. Base level as the ideal limit for erosion. The story of the great unconformities. Discovery of the vast sedimentary record in Grand Canyon. Recognition of volcanic episodes. Basic understanding of the geologic structures of the plateaus. All of these ideas have been expanded and modified by later geologists. But the science of Earth history owes much to this man, who first showed the way through the great unknown.  John Wesley Powell, geologist.