The geology of Oregon is for the most one of ancient lakes and seabeds. Sedimentary deposits laid down over millions of years with intrusions of basalt into the sediments and lava extrusions over. The seas covered most of Oregon well into the Eocene when the Cascade range began to build. However, the Willamette Valley and the western part of the state was alternately uplifted and flooded. We are of course speaking of time so vast as to be abstract. It is possible to see time in the remnants of geologic formations. Still those eons are only period names that represent the growth rings of the land.

The volcanism of the Northwest reaches back to the Triassic Period 230 million years. The Klamath Mountains of Southern Oregon and the Blue Mountains in Eastern Oregon date to the Jurassic Period. These granite batholith formations are unique. The formations that are most obvious and more easily sighted are much younger. The Columbia River Basalt whose 2,000-foot cliffs line the Columbia River gorge is notable. These flows stretch west to Astoria and East to the Blue Mountains. Dated approximately 60 million years old, it overlays the volcanoes of the Eagle Creek formation. Modern day peaks like Pepper Mt., Mt. Pleasant, Beacon Rock and Mt. DeFrance are the cones of the Eagle creek formation. The more familiar volcanoes of the Cascade Range. Mt. St. Helens, Mt. Hood and Mt. Adams sit on top of the Columbia river basalt. In fact, there is more than just one lava formation. The western slope of the Cascades is composed of at least three flows subsequent to the Columbia River Basalt formation. The first lava cones began their eruptions in the Pliocene Epoch some 10 million years ago. Not to say that these volcanoes continued erupting on into the Pleistocene, but those we see today are rooted in the lava flows of those extinct landmarks. The continuing output of the Cascades indeed has carried into the present day. Mt. Mazama, Crater Lake, exploded at about 6,600 years ago, well into the period of exploration and settlement by Native Americans. The 1980 eruption of Mt. St. Helens shows two things, that the vulcanism of the Pacific northwest continues and that geologic time is not the same as our time.

Columbia River

Cutting through all of this is the Columbia River, I can not speak of the Northwest without mentioning the great river. It's headwaters lie far to the north in the icefields of the Canadian Rockies. The actual area it drains is huge. The mountains of southern Yellowstone, the Grand Tetons, Northwestern Montana, all of Idaho, Washington state east of the Cascades, Oregon, east and west of the Cascades. Even the humble little South Yamhill flows east from the coastal mountains to the Columbia River by way of the Willamette River. The main stem of the Columbia has a flow rate of 150,000 cubic feet per minute near the Tri-Cities in Washington state. The importance of the measurement at that place is twofold. First, it is the last free flowing stretch of the Columbia River. Second, it is just north of its confluence with the Snake River. The Snake River flows south from the Yellowstone plateau past the Grand Tetons across southern Idaho into Hell's Canyon. The wild Salmon River of Idaho with its three forks, joins the Snake just north of that canyon. The Clearwater River flows into the Snake River at Lewiston and Clarkston. The Snake River then turns southwest and cuts through the Columbia Basalt formation of Eastern Washington, then into the Columbia River at Burbank, Washington. It was at that point in 1804 that Captain Lewis, as in Lewis and Clark, finally realized that there was no direct water route to the Pacific.

The significance of the Columbia River on western Oregon is subtle but worth mentioning. During the last ice age, an ice dam across Clarks Fork River in Montana raised ancient Lake Missoula. Lake Missoula was of such a size that even today its ancient shoreline is visible on the mountains of western Montana. A thousand feet and more above the Flathead Valley this great lake broke through that ice dam and poured north into the Columbia River. Another ice dam near the present day Grand Coulee forced the flood waters south across the Columbia Basalt formations of the Columbia Basin in Washington state. The flood turned west through the Columbia gap and scoured the Columbia River Gorge to its present day configuration. The amount of water was overwhelming. The suddenness with which it happened was paralyzing. There was so much water that at Portland where the Columbia turns north, the river backed up and flooded the Willamette Valley. We know this from the great number of boulders that were carried with the floodwaters and deposited here when the water drained. An exceptional video produced by Washington State University at Pullman, Washington gives greater detail than I am able to relate. The flood, of which there was more than one, is of recent origin. Along with the ongoing eruptions of the Cascade Mountains, the flood impacted not only the land but also the people who had by then moved south from the Bering land bridge and into the Americas.

This brings us to the life that existed as part of the landscape. This life was diverse, sponges and corals of the Triassic Period were common when all of Oregon was a sea. Flora too was abundant and varied, the fossils of tree ferns and palms attest to the warmer climate of the Jurassic times. Petrified Ginkgo trees are spread across the Pacific Northwest. Sub-tropical plants; figs, avocados, palm trees grew across Central Oregon. Animal life continued to prosper and over the fifty million years from the Eocene to the Pliocene, we see a progression of fauna. The evolution of the horse is contained in the region's fossils. The four toed horse of the Eocene slowly becomes the three toed horse and finally the animal we're familiar with today. Giant pigs, saber toothed cats, tiny camels, rhino's wolves, antelope, mastodons, all left visible remains.

An excellent place to view many of these past residents is the John Day fossil beds of North Central Oregon. Located south of Interstate 84 at the eastern end of the Columbia Gorge the interpretive center shows many of these items.

Mastodon finds are common. The Tri-Cities are of Washington State is a good example. The bones of more than a few have been found in that area. One specimen was uncovered near West Richland. Another near Wallula was excavated only three or four years ago. It is more than probable that they were caught and buried in the great Missoula floods. The dates of 11,000 years seem to match.

Another recent find was that of a human skeleton along the banks of the Columbia River in the same general area. Named "Richland Man," studies are currently under way to determine ethnology and a time frame. Human habitation of this area has been dated to 13,000 years ago. That time is more likely too close and represents only occupied sites. There are some caves in Eastern Oregon near the shores of ancient Lake Bonneville and with the proper excavation may establish native habitation prior to 15,000 years ago. I personally believe that the chauvinism of scientists and the Euro-centric belief of human civilization will preclude those discoveries. It is possible that the great cataclysms of the Northwest have erased meaningful traces of human habitation. Still I do wonder.

The recent history of human occupation in the Willamette Valley is dated only a few hundred years. Excavations of sites in the Willamette Valley and Coastal Oregon show a common link with the Chinook Tribe of Southwestern Washington. The five tribes of the Grand Ronde are distinct, but ethnological and artifact studies of sites excavated go a long distance in showing familia (tribal) migration, brought about perhaps by population pressures on local food supplies.

The first contact with Europeans and Northwest Coastal natives was in the early 1770's. Juan Josef Perez under orders from Philip III of Spain sailed into the area and claimed the territory for Spain. Captain Cook's voyage of exploration sailed through the area in the late 1770's. In fact, many of the landmarks today were named by him, Puget Sound, Mt. Rainier, and so on. Captain Gray sailed up the Columbia River as far as present day Portland by 1800. It was his reconnaissance that led Jefferson to believe that the Columbia was that mythical transcontinental waterway that explorers since Columbus had sought.

There is of course much more, and we hope you check in with us in the future for updates and features about the geology, floral, fauna and humanity of this area.

Michael Sherer

Consider novels by Naomi Sherer available on Amazon

Sagesong cover Rise to the Occasion cover
Coming Soon: Beyond Namche, The Open Door, Wildly in the Rockies




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Last Modified: Monday, 29-Jun-2009 11:26:26 EDT