The story of the forces which have created the landscape of what is currently eastern Washington state has to be some of the weirdest in recent geologic history.
The north Cascades were volcanic WAY back when apparently they were sitting atop an island (Japan- or New Zealand-sized?). This island microcontinent drifted across the Pacific from Asia (its fossils of a certain era match those of southeast Asia, rather than North America) and eventually docked here, sometime during the long epochs of the dinosaurs. There are incredible fossilized palm trees from a dig near Bellingham (just south of the Canadian border, for those of you not from around here), tantallizing clues to the Cascades past as a balmy tropical island. The swampy edges of this island, comressed over the eons, left behind layers of coal, now tilted to 40 degrees underfoot. Some of those swamps wound up in Renton Hill, two or three miles south of our house. And some of it ended up about three miles northeast of our house in what has been fairly recently renamed Cougar Mountain, in the aptly monikered town of Newcastle. (Our little house is perched on the crest of a hill at 200 feet above sea level and five miles due east of Puget Sound - which is more or less a large, wide fjord.)
The land to which the Cascade microcontinent docked was apparently another island which had docked even longer ago, which is referred to as the Okanogan microcontinent. (Apparently the history of the West Coast from Mexico up to Alaska involves many microcontinent collisions, much the same as the larger collision of the Indian subcontinent with Asia, currently pushing the Himalayas star-ward at some inches per year.) Before these Pacific islands rode the continental drift conveyor belt, the coastline of North America ran just west of the current Idaho-Washington state line.
Apparently, sometime after the Cascade island became part of North America, it seems that the volcanos turned off for a long epoch and eroded away. And enormous lava flows turned on in what is now the Columbia Plateau. There may have been as many as fifty of these firey diluvian flows over some millions of years, which buried an unfathomable swath of territory in Idaho, Washington, Oregon, along with bits of British Columbia and Montana. Between flows, life would return to the cooled land during 200,000-year intervals of peace. It was one of these red-hot flows which swept through a lake in what is now Ginko Petrified Forest State Park, a two- hour drive east of our house, burying an unbelievably wide variety of mostly deciduous trees lying soaked in the lake bottom. (We drove out to see this on Saturday.) The water which impregnated the logs, leaves, branches, and seeds spared them from becoming instant ash, and over some decades, they were petrified, preserving them in exquisite detail. Species have been unearthed here from 25 separate genre, including elm, walnut, oak, fir, and ginko. Ginko, although once widespread throughout the world, is now extinct everywhere except east Asia; ginko preserved as cultivars in temples there have been reintroduced around the planet.
If you have ever seen the dry, dry high desert of today's Columbia Plateau, you might find the Miocene forests and rivers, and lakes resenbling those of the America Southeast, inhabited by elephants and rhinoceros, quite shocking. The Cascades were much lower at that time, owing to an earlier phase in the uplift than we are witnessing today, and they did not force the clouds blowing in daily off the Pacific to drop their precious cargo as rain and snow before reaching the Plateau, as they do now.
After all of this very occasional and unbelievably widespread volcanic carnage was finished (the spot where the visitor center for the state park stands is atop 5000 feet of volcanic rock, and in some other places stands two miles thick!), the Ice Age rolled through, creating some of the weirdest flooding ever discovered by geolgists. At the glacial maximums, glaciers incurred all the way through Canada and across the north edge of Washington state, with a large lobe down the west, which carved out numerous features, including the 13-mile-long Lake Washington, sitting at the bottom of our hill. Lake Washington was once salt water, connected to the sea; scientists and native folklore both attest to this. It was perhaps an eruption of Mt. Rainier which cut it off from the rest of the Sound and made it into a freshwater lake.
In Ice Age Montana, there was an enormous valley which slowly filled with water, dammed at one end by glacier; this high altitude body of icy freshwater was called Glacial Lake Missoula. When it filled far enough, it would float its glacier,, breaking the seal and spill out, rushing across Idaho and Washington, through the great Columbia River Valley to the sea. The volume of swirling, muddy water was absolutely unprecedented, and it would form several temporary lakes on its way out: temporary lakes the size of the entire Willamette River Valley, stretching down to southern Oregon. Eastern Washington is covered with enormous, dry water features - waterfalls which would dwarf Niagara, creeks and river beds and canyons, all of which house little to no water today. This flood did not happen just once, but possibly as many as twenty-five times over the eons!
The desert holds much intellectual fascination for me, but I feel a tidal pull back to the green. After our afternoon at Ginko/Wapanum State Park, we drove west into the eastern, drier edge of the Cascades, and camped in the piney Teanaway Community Forest.
If you happen to be on Facebook, I will post a whole pile of photos there by way of illustration from our weekend adventure.