The Emerald Mile: The Epic Story of the Fastest Ride in History Through the Heart of the Grand Canyon by Kevin Fedarko Page B
Authors: Kevin Fedarko
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engine that drives almost all of this activity is snow. This means that the bulk of the Colorado’s discharge tends to come down in one headlong rush. Throughout the autumn and the winter, the river might trickle through the canyonlands of southern Utah at a mere three thousand cubic feet per second. With the melt-out in late May and early June, however, the river’s flow can undergospectacular bursts of change.In the space of a week, the level can easily surge to 30,000 cfs, and a few days after that it can once again rocket up, surpassing 100,000 cfs. Few rivers on earth can match such manic swings from benign trickle to insane torrent. But the story doesn’t end there, because these savage transitions are exacerbated by yet another unusual phenomenon, one that is a direct outgrowth of the region’s unusual climate and terrain.
On most sections of the Colorado Plateau, rainfall is sparse and infrequent. Many areas receive less than six inches a year, roughly equivalent to what falls on Africa’s Kalahari Desert. It is not unusual, however, for almost the entireannual quota to fall during a single storm or two—brief but exceptionally violent and highly localized cloudbursts that hammer into the dry dirt like a power washer. With so little vegetation to hold that dirt in place, the loose soil is swept into the canyons in muddy torrents, creating flash floods that transfer colossal loads of sediment directly into the river, turning it the color of chocolate. Rolling with a muscular, heavy viscosity that makes it seem more solid than liquid,the river annually removes nearly sixty dump trucks of sediment for each square mile within its watershed, dismantling the landscape grain by grain, pebble by pebble, and freighting the entire mass toward the Sea of Cortés.
As a result, the Colorado is one of the siltiest rivers in the world. It’s probably safe to say that no other river anywhere can matchthe compulsive intensity with which it cuts away the topography and bulldozes those materials downstream. Prior to 1963, the year that the Glen Canyon Dam was finished, the Colorado hauledan average of nearly half a million tons of sand and silt past Yuma, Arizona, sixty miles upstream from the river’s mouth, every twenty-four hours. (Its record, set in 1927, was more than twenty-seven million tons of sand and silt in a single day. ) The Nile and the Mississippi are both renowned for their alluvial deltas, but the Colorado’s silt-to-water ratio leaves them in the dust. A single cubic foot of the semisolid Colorado isseventeen times more silt-laden than the so-called muddy Mississippi, a river that carries twenty-four times more volume and drains an area five times the size of the Colorado’s basin. And for every acre-foot of water—defined as a unit of water equal to one acre covered one foot deep—the Colorado freights eleven tons of silt. One way of putting this into perspective is to consider that France and the United States together excavated 357 million tons of dirt while digging the Panama Canal, during roughly fifteen years of total labor. In Powell’s day, the ancestral Colorado was capable of transporting the same amount of soil, by weight, in less than a fortnight.
The virgin Colorado was so saturated with silt that, during certain times of the year, only about 48 percent of the cocoa-colored slurry sluicing past Lee’s Ferry was actually composed of water. Among the handful of settlers who first lived within the canyon country during the nineteenth century, it was said that the river was “too thick to drink and too thin to plow.” Others joked that on windy daysdust could be seen blowing off the water’s surface. This was no laughing matter, however, to the Mormon sheepherders who attempted to ford their flocks at Lee’s Ferry and stood helplessly as the animals sank beneath the surface, pinned down by the weight of the sediment trapped in their wool.
This unusual combination of gradient, volatility,
On most sections of the Colorado Plateau, rainfall is sparse and infrequent. Many areas receive less than six inches a year, roughly equivalent to what falls on Africa’s Kalahari Desert. It is not unusual, however, for almost the entireannual quota to fall during a single storm or two—brief but exceptionally violent and highly localized cloudbursts that hammer into the dry dirt like a power washer. With so little vegetation to hold that dirt in place, the loose soil is swept into the canyons in muddy torrents, creating flash floods that transfer colossal loads of sediment directly into the river, turning it the color of chocolate. Rolling with a muscular, heavy viscosity that makes it seem more solid than liquid,the river annually removes nearly sixty dump trucks of sediment for each square mile within its watershed, dismantling the landscape grain by grain, pebble by pebble, and freighting the entire mass toward the Sea of Cortés.
As a result, the Colorado is one of the siltiest rivers in the world. It’s probably safe to say that no other river anywhere can matchthe compulsive intensity with which it cuts away the topography and bulldozes those materials downstream. Prior to 1963, the year that the Glen Canyon Dam was finished, the Colorado hauledan average of nearly half a million tons of sand and silt past Yuma, Arizona, sixty miles upstream from the river’s mouth, every twenty-four hours. (Its record, set in 1927, was more than twenty-seven million tons of sand and silt in a single day. ) The Nile and the Mississippi are both renowned for their alluvial deltas, but the Colorado’s silt-to-water ratio leaves them in the dust. A single cubic foot of the semisolid Colorado isseventeen times more silt-laden than the so-called muddy Mississippi, a river that carries twenty-four times more volume and drains an area five times the size of the Colorado’s basin. And for every acre-foot of water—defined as a unit of water equal to one acre covered one foot deep—the Colorado freights eleven tons of silt. One way of putting this into perspective is to consider that France and the United States together excavated 357 million tons of dirt while digging the Panama Canal, during roughly fifteen years of total labor. In Powell’s day, the ancestral Colorado was capable of transporting the same amount of soil, by weight, in less than a fortnight.
The virgin Colorado was so saturated with silt that, during certain times of the year, only about 48 percent of the cocoa-colored slurry sluicing past Lee’s Ferry was actually composed of water. Among the handful of settlers who first lived within the canyon country during the nineteenth century, it was said that the river was “too thick to drink and too thin to plow.” Others joked that on windy daysdust could be seen blowing off the water’s surface. This was no laughing matter, however, to the Mormon sheepherders who attempted to ford their flocks at Lee’s Ferry and stood helplessly as the animals sank beneath the surface, pinned down by the weight of the sediment trapped in their wool.
This unusual combination of gradient, volatility,
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