THE GREAT RIVER OF THE WEST was born from violence, from fire, and from ice. Fire came first. More than 250 million years ago, when most of the landmass of Earth was contained within the supercontinent Pangea, superheated liquefied rock, magma, burned a three-pronged rift through the crust and began the tectonic separation of North America, Europe, and Africa. As the new continents drifted apart, somewhere between one hundred million and ninety million years ago, the movement of plates floating atop a fiery mantle pushed long chains of active volcanoes hard against the upper left edge of North America, a scorching fusion that created what is now the Pacific Northwest.
The future basin of the Great River was surrounded then by the continuously bubbling, spewing, spreading eruptions of the young mountains that shaped the original configuration of a track flowing out of what is now Canada toward the Pacific Ocean. It was the molten lava that pulled the moisture out of the Earth’s interior and left water on the planet’s surface as it cooled. An ancestral version of the river was soon descending from a long, sunken fault line that would become the Rocky Mountain Trench.
The Rockies themselves rose as massive upwelling explosions between eighty and fifty-five million years ago, and off their western flanks sent huge flaming flows of basalt lava south to push out an inland sea and shape the path of the still-forming Great River beneath it. The Cascade Mountains are much younger than the Rockies—they did not uplift out of the Earth’s mantle until five to four million years ago—but they were also enormous fulminations that further seared and shifted the region’s topography, helping to define the outline of an immense waterway.
Then, about thirty-three thousand years ago, North America’s volcanic fires were overtaken by a rapid expansion of ice spreading south, caused, scientists believe, by a shift in the Earth’s orbit around the sun. Five thousand years later, much of North America was under two enormous ice sheets. The one to the west, the Cordilleran, covered at its maximum nearly two million square miles of land, stretching from Alaska to Montana, and may have reached as far south as the northeast corner of Oregon.
That ice is what put the finishing touches on the formation of the Great River. The gouging of glaciers moving south and west did a good bit of the work, but it was the melting of the ice that had the greater effect. Around nineteen thousand years ago, when the glaciers began to once again retreat, a gigantic frozen wall, an ice dam, embanked an enormous body of fresh water that geologists call Glacial Lake Missoula. The gargantuan pond was two thousand feet deep then and about the size of today’s Lake Ontario. On at least forty occasions between nineteen and thirteen thousand years ago, the ice dam that held back Lake Missoula failed. The resulting floods were epic on a scale that defies human imagination. Each one unleashed more water than was in all of the Earth’s rivers combined, scouring its way through mountain ranges to inundate an area of sixteen thousand square miles to a depth of up to several hundred feet. In the center of the flood path was what would become the bed of the Great River. When the waters receded, the ultimate course of that river, and of its connection to a vast system of tributaries, was left behind.
Where the river began then was where it does now, spilling out of the remnant of a smaller glacial lake that had been swept up into the Lake Missoula floods. Situated today in southwestern Canada, the lake bears the name of the river it has spawned, Columbia.
Given the underl