At the climax of the Ice Age a massive glacier came face-to-face with the ancient basement rock of North America. Something had to give.

The nature of nature is that the new is generally trying to devour the old. In geology, the engine for this perpetual drama is largely hidden by seawater. In mid-ocean ridges volcanic forces push fresh terrain outward, creating huge plates of fresh rock that behave like slow-moving conveyer belts. When the plates inevitably collide, terrain buckles and melts under pressure, pushing up mountains and volcanoes, and lava.

A corollary to this overview are longstanding, stationary hot spots on the surface crust that convey blowtorch heat from the earth’s mantle. One such hot spot continues to create the Hawaiian islands. Another currently lies beneath the actively steaming caldera at Yellowstone National Park. On a map the Yellowstone hot spot appears to be moving eastward, but this is only because the North American plate is moving to the southwest.

Some 16 million years ago, the hot spot now beneath Yellowstone was situated about where corners of Idaho, Oregon and Nevada intersect today. Geologists think this is the reason more than 50,000 cubic miles of lava (basalt) spewed from hundreds of surface vents in western Idaho, northeast Oregon and southeast Washington. The peak of the vent eruptions was between 14 and 16 million years ago—with continuing smaller eruptions until about 5.5 million years ago.

The result is the black and brown bedrock that spans the lower Columbia basin and, in some places, is more than 10,000 feet thick. Basalt makes for beautiful palisades and dramatic rimrock cliffs and is otherwise ubiquitous in the lower Columbia Basin and through the Columbia River gorge. Witness, for example, the natural columns in road cuts around Spokane’s international airport. Yet, it would be a far less visible feature of the landscape were it not for Ice Age floods that violently stripped away the overlying topsoil.

On Green Monarch Ridge you can easily see and touch the ancient rock in outcroppings where the Purcell Trench ice lobe repeatedly rammed and sealed itself onto the mountainside, perhaps as recently as 14,000 years ago.

In geologic terms, it’s as though all of this just happened. If you condensed Earth history into a day, the basalt flows would have occurred in the last 5 seconds and the peak Ice Age floods in the last blink of an eye. But it’s eloquent, and perhaps fitting, that at least one character in the Bretzland story is over a billion years old and that you can still see it and touch it.

To do so, you’ll have to drive to Idaho and, lucky you, visit one of the Pacific Northwest’s most beautiful places, east of Sandpoint. Whether you get to Sandpoint via U.S. route 2, or U.S. 95, you’ll be headed toward a junction, north of town, where you’ll want to pick up Idaho state route 200. Route 200 follows the shoreline of Lake Pend Oreille which bends east and then southeastward toward the town of Clark Fork, where the Clark Fork River empties into Lake Pend Oreille.

Along the way, a good place to stop, enjoy the view, have a picnic and gather your bearings is the Trestle Creek beach and campground about ten miles out from Sandpoint.

At the shoreline, the view to the right (west) takes in the Selkirk Mountains and the slopes of the fabled Schweitzer Mountain ski resort. In the other direction, to your left, you can see the northernmost mountains of the Bitterroot Range, including Green Monarch Ridge with its western face plunging steeply into the lake. As unlikely as it may seem, this tranquil scene was ground zero for the epic floods that created Washington’s channeled scablands.

At a lakeside turnout a few more miles down the highway, just before the town of Hope, there is a roadside educational display. One of the large display panels tells the story of the Purcell Trench glacier arriving from the north—as tall as four Space Needles stacked atop one another—and pushing up against Green Monarch Ridge.

The massive glacier was unrelenting, but the Green Monarchs are built from some of the oldest and hardest rock in North America. These are layers of ancient sedimentary and metamorphic rock that accrued in what is known as the Belt Basin, essentially a vast inland sea that formed more than a billion years ago near the westernmost edge of what eventually became the North American craton. Belt Basin rocks are commonly referred to as the Belt Supergroup in the U.S. and the Purcell Supergroup in Canada.

Here’s a fun fact. When you’re done perusing the educational signs at the turnout near Hope, just turn around so that you’re looking across the highway. In the road cut beyond the westbound lane you’ll notice layers of exposed rock that are predominately the color of copper but with streaks of tan, white, gray and a dark chocolate shade of brown. It’s not just any rock. It’s an outcrop of the Prichard Formation which is the very basement of the Belt Basin, the oldest rock formation in western North America.

When the Purcell Trench ice sheet met the incredibly hard and old rocks at Green Monarch Ridge the collision created a seal—a natural ice dam 2,000 feet high, trapping the Clark Fork River in its valley. Consequently, a massive body of water, glacial Lake Missoula, built up behind the ice dam. Missoula, Montana, is nearly 200 miles southeast of the Clark Fork ice dam. There is clear evidence that the trapped floodwaters at Missoula were nearly 1,000 feet deep.

Under such accumulating pressure, the Clark Fork ice dam would periodically disintegrate (with a roar on par with a massive volcanic eruption or asteroid strike) sending an inland tsunami of ice-laden floodwaters racing toward Spokane at highway speeds. Based on the field evidence downstream, geologists think this happened not once, but at least dozens of times.

J Harlen Bretz put forth his theory of catastrophic flooding as the cause for the epic erosional features of Washington’s channeled scablands in 1923. He soon began referring to it as “the Spokane flood.” This is because it was obvious, at least to him, that the Spokane area had been a bottleneck through which most of the floodwaters had passed. According to Bretz’s biographer, John Soennichsen, the geologist was aware of ancient Lake Missoula by 1925. Yet he was reluctant, for several years, to connect the dots.

What what would eventually turn the tide was a finding that another northwest geologist, J.T. Pardee, first shared at a Seattle conference in 1940. There were giant ripple marks on Montana’s Camas Prairie northwest of Missoula. Pardee proposed that the fifty foot-high ripples were the result of sudden, massive draining of Lake Missoula—with the waters clearly heading westward, toward the Columbia Basin. Without explicitly saying so, Pardee was presenting the missing piece that clearly validated Bretz.

The scale of the story can be mind-boggling. It was a cataclysmic event that spanned time zones, a great wave of devastation the followed the curve of the planet from the alpine beauty of the northern Rockies to the bare hills and sage of the Pasco Basin, and the Columbia Gorge beyond.

Had Bretz’s great flood theory of the scablands been less controversial, Pardee’s finding (formalized in a 1942 paper) would have abruptly ended the debate. Yet—as Soennichsen recounts in his fine book Bretz’s Flood—the controversy dragged on for decades. It was a hollow debate which had far less to do with the geologic evidence than with the stature and hubris of the prominent geologists who’d dismissed Bretz’s theory from the start.

With science alone, it is difficult to capture the scale of the story, although I think you’d agree that the road turnout signs on Highway 200 near Hope do a pretty job, especially given the space limitations. The scale can be mind-boggling when one ties to comprehend a cataclysmic earth story that spans time zones, following the curve of the planet from the alpine beauty of the northern Rockies to the bare hills and sage of the Pasco Basin, and the Columbia Gorge beyond.

The timescale is also mind-bending. Bretz was nearly 100 years old when he passed and well into his late nineties when he was given his profession’s top award, finally recognizing his persistence and the quality of his work. It was a vindication that took far too long given the relative brevity of a human life.

On Green Monarch Ridge you can easily see and touch the ancient rock in outcroppings where the Purcell ice lobe rammed and sealed itself onto the mountainside, perhaps as recently as 14,000 years ago, maybe less.

Some of the intransigent rocks that greeted the ice front are 1.3 billion years old. Despite the current, human-induced warming trend, it’s likely there will be other Ice Ages, and more ice-damming collisions between the face of the Purcell Trench glacier and the Belt Basin rocks on Green Monarch Ridge. It’s the kind of long story that can repeat itself.

Time for lunch.

–tjc