If Oregon were part of a jigsaw puzzle of the United States, it would be a squarish piece with a divot carved out of the center top. To the west is the Pacific Ocean, with some 370 miles of beaches, dunes, and headlands; to the east are the Snake River and Idaho. Up north, much of the boundary between Oregon and Washington is defined by the mighty Columbia River, while southern Oregon lies atop the upper borders of California and Nevada.
Broad rows of mountains divide the coast from the inland valleys, and western Oregon from the central and eastern parts of the state. East of the highest central range the Columbia Plateau predominates, broken up in the northeast where mountainous features reassert themselves. In the southeast, scattered lakes dot the landscape, and fault-block mountains gently ascend on one slope, then drop sharply off.
The Great Basin desert—characterized by rivers that evaporate, peter out, or disappear into underground aquifers—makes up the bottom corner of eastern Oregon. Here the seven-inch annual rainfall of the Alvord Desert seems as if it would be more at home in southeastern California and Nevada than in a state known for blustery rainstorms and lush greenery.
Highs and Lows
Moving west to east, the major mountain systems start with the Klamath Mountains and the Coast Range. The Klamaths form the lower quarter of the state’s western barrier to the Pacific; the eastern flank of this range is generally referred to as the Siskiyous. To the north, the Oregon Coast Range, a younger volcanic range, replaces the Klamaths. The highest peaks in each of these cordilleras barely top 4,000 feet and stand between narrow coastal plateaus on the west side and the rich agricultural lands of the Willamette and Rogue Valleys on the other. Running up the west-central portion of the state is the Cascade Range, which extends from Northern California up to Canada. Five of the dormant volcanoes in Oregon top 10,000 feet above sea level, with Mount Hood, the state’s highest peak, at 11,239 feet.
Beyond the eastern slope of the Cascades, semiarid high-desert conditions contrast with the Coast Range rain forests and the mild, wet maritime climate that characterizes much of western Oregon. In the northeast, the 10,000-foot crests of the snowcapped Wallowas rise less than 50 miles away from the hot arid floor of Hells Canyon, itself about 1,300 feet above sea level.
In addition to Hells Canyon, the country’s biggest hole in the ground (7,900 feet maximum depth), Oregon also boasts the continent’s deepest lake: Crater Lake, with a depth of 1,958 feet.
Last of the Red-Hot Lavas
Each part of the state contains well-known remnants of Oregon’s cataclysmic past. Offshore waters here feature 1,477 islands and islets, the eroded remains of ancient volcanic flows. Lava fields dot the approaches to the High Cascades. East of the range, a volcanic plateau supports cinder cones, lava caves, and lava-cast forests in the most varied array of these phenomena outside of Hawaii.
The imposing volcanic cones of the Cascades and the inundated caldera that is Crater Lake, formed by the implosion of Mount Mazama some 6,600 years ago, are some of the most dramatic reminders of Oregon’s volcanic origins. More fascinating evidence can be seen up close at Newberry National Volcanic Monument, an extensive area south of Bend that encompasses obsidian fields and lava formations left by massive eruptions. (Incidentally, geologists have cited Newberry on their list of volcanoes in the continental United States most likely to erupt again.) Not far from the Lava Lands Visitor Center in the national monument are the Lava River Cave and Lava Cast Forest—created when lava enveloped living trees 6,000 years ago.
Earthquakes and Tsunamis
Scientists exploring Tillamook County in 1990 unearthed discontinuities in both rock strata and tree rings indicating that the north Oregon coast has experienced major earthquakes every several hundred years. They estimate that the next one could come within our lifetimes and be of significant magnitude. In this vein, Japanese scientists maintain that a 9.0 quake struck the Northwest coast in 1700, based on tsunami records indicating that 6–9-foot-high tidal waves hit Japan’s coastline. This date is also consistent with Northwest Native American oral histories and geological evidence.
These coastal quakes are caused by subduction, which occurs when one of the giant plates that make up the earth’s crust slides under another as they collide. In Pacific Northwest coastal regions, this takes place when the Juan de Fuca plate’s marine layer is pushed under the continental North American plate. With virtually every part of the state possessing seismic potential that hasn’t been released in many years, the pressure along the fault lines is increasing.
In coastal areas, one of the greatest dangers associated with earthquakes is the possibility of tsunamis. The waves are produced by an offshore quake—even one centered thousands of miles away. As a tsunami draws closer to shore, driven by the force of the quake, it takes in preceding water and builds into a series of waves traveling as fast as 500 miles per hour and reaching as high as 100 feet. Ever since a tsunami unleashed by Alaska’s 1964 quake (measured at 14.2 feet high at the mouth of the Umpqua River) resulted in four casualties in Beverly Beach and over $1 million in damage, local authorities have made seismic preparedness a priority, with a system of warning sirens and evacuation signs pointing the way to higher ground.
The Great Meltdown
However pervasive the effects of seismic activity and volcanism are, they must still share top billing with the last ice age in the grand epic of Oregon’s topography.
At the height of the most recent major glaciation, the world’s oceans were 300–500 feet lower, North America and Asia were connected by a land bridge across the Bering Strait, and the Oregon coast was miles west of where it is today. The Columbia Gorge extended out past present-day Astoria. As the glaciers melted, the sea rose.
When that glacial epoch’s final meltdown 12,000 years ago unleashed water dammed up by thousands of feet of ice, great rivers were spawned and existing channels were enlarged. A particularly large inundation was the Missoula Flood, which began with an ice dam breaking up in what’s now northern Idaho. Floodwaters carved out the contours of what are now the Columbia River Gorge and the Willamette Valley. Other glacial floodwaters found their outlet westward to the sea, digging out silt-ridden estuaries in the process. Pacific wave action washed this debris back up onto the land, helping to create dunes and beaches.
by Judy Jewell and W. C. McRae from Moon Oregon, 8th Edition, © Elizabeth & Mark Morris and Avalon Travel