Geology Reference
In-Depth Information
recently to stand shoulder to shoulder with its elder sibling to the north. Sometimes conflict
is all about perspective.
We descended the Cascades and soon entered the high desert of eastern Washington. The
temperate rainforest of western Washington was miles behind us, and the lack of plants
made it easy to see the landforms. Once across the Columbia River we continued eastward,
driving up onto a plateau where swirling winds blew soil off freshly plowed fields. Racing
the dust devils, we dropped into Moses Coulee, a canyon with vertical walls of layered
basalt half buried beneath talus ramps. Nothing had removed the rocks that fell to the valley
floor. They just piled up in place, right where gravity left them.
We stopped, gathered the students on a small rise, and asked them how the canyon was
formed. They immediately ruled out wind and glaciers. The valley was not U-shaped like
typical glacial valleys, and none of us could imagine how wind might gouge a canyon out
of hard basalt. But neither did anyone see a river or stream. After a while I pointed out
that we were standing on a pile of gravel and asked the class to explain how these rounded
granite pebbles came to be there when the closest source of granite lay over the horizon.
Silence.
Hiking through eastern Washington canyons littered with exotic boulders has long been
a standard field trip for beginning geologists. It takes a while to register what you see
there: the water-scoured cliff of a now dry waterfall hundreds of feet high in the middle of
the desert; giant potholes where no river flows today; granite boulders parked in a basalt
canyon. Gradually, the contradictions fall into place and answer the questions of where car-
sized wayward boulders came from and what was the source of the water that moved them
around and carved the falls. Students can conjure up eastern Washington's giant floods
once their professors give them the clues. Once you know what to look for, the evidence is
hiding out in the open in plain sight. But the idea of a great flood capable of gouging deep
valleys into hard rock seems unlikely in the middle of a desert, particularly when you've
been taught that such a thing is impossible.
After European geologists dismissed a central role for a catastrophic flood in earth his-
tory, the idea became geological heresy. Although J Harlen Bretz uncovered evidence of
giant floods in eastern Washington in the 1920s, it took most of the twentieth century for
