A Self-Guided Tour of the Geology of the Columbia River Gorge— Portland Airport to Skamania Lodge, RESOURCES Stevenson, Washington by David K. Norman and Jaretta M. Roloff WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Open File Report 2004-7 March 2004 NATURAL trip location DISCLAIMER Neither the State of Washington, nor any agency thereof, nor any of their em- ployees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any informa- tion, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or other- wise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the State of Washington or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the State of Washington or any agency thereof. WASHINGTON DEPARTMENT OF NATURAL RESOURCES Doug Sutherland—Commissioner of Public Lands DIVISION OF GEOLOGY AND EARTH RESOURCES Ron Teissere—State Geologist David K. Norman—Assistant State Geologist Washington Department of Natural Resources Division of Geology and Earth Resources PO Box 47007 Olympia, WA 98504-7007 Phone: 360-902-1450 Fax: 360-902-1785 E-mail: [email protected] Website: http://www.dnr.wa.gov/geology/ Cover photo: Looking east up the Columbia River Gorge from the Women’s Forum Overlook. Crown Point and its Vista House are visible on top of the cliff on the right side of the river. I-84 runs below. Cape Horn is the sheer section of cliffs slightly upriver and across from Crown Point. Published in the United States of America A Self-Guided Tour of the Geology of the Columbia River Gorge— Portland Airport to Skamania Lodge, Stevenson, Washington by David K. Norman and Jaretta M. Roloff WASHINGTON DIVISION OF GEOLOGY AND EARTH RESOURCES Open File Report 2004-7 March 2004 Stevenson (Skamania 5 503 River Table Lodge) Mountain (V4) SCENIC AREA Bonneville 500 Mount Mount North Cascade Locks Dam exit 44 St. Helens Adams Bonneville Bridge of the Gods Beacon Rock (toll $1.00) Columbia Washougal exit 41 Vancouver Skamania NAT’L Willamette Mount (V3) Washougal 14 GORGE Eagle Zion exit 35 Dodson Portland Camas 30 Cape International Horn Stop 2 Creek Airport exit 31 Rocky River Multnomah Butte exit 18 exit 22 exit 25 Falls 84 30 (V2) COLUMBIALarch RIVER (V1) Stop 1 Mountain Portland Mount Mount Kelly Troutdale Crown Corbett River Tabor Butte Point Hood 45°30¢ River Pepper 205 Mountain Gresham Sandy Run Bull Run Reservoir ii 26 River Bull 122° Lake Oswego Boring Figure 1. Location map. A Self-Guided Tour of the Geology of the Columbia River Gorge—Portland Airport to Skamania Lodge, Stevenson, Washington Prepared for the Association of American State Geologists 96th Annual Meeting, June 13–16, 2004 General Directions from the Airport to Skamania NORTH AMERICAN PLATE Lodge (N45°41¢12.8² W121°54¢21.5²) (Distance ap- fracture zone Mount proximately 42 miles): Leave the airport via I-205 Garibaldi convergence South. Exit to Interstate 84 East (toward The Dalles) CANADA (Fig. 1). Continue east on I-84 until the Cascade Locks/ U.S. Bridge of the Gods/Stevenson exit (44). Take the Mount Baker Glacier Bridge of the Gods over the Columbia River ($1.00 Peak OLYMPIC MOUNTAINS RANGE toll), then turn right (east) onto Highway 14. Travel a zone Seattle short distance (1.5 mi from the Bridge of the Gods to JUAN PACIFIC PLATE Mount DE FUCA Rainier milepost 43 of Highway 14). Turn left onto Rock Creek PLATE Olympia fore–arc Drive. Proceed 0.2 mi to the entrance to Skamania Yakima Juan de Fuca Ridge faults and Lodge (on the left). folds Mount CASCADE spreading zoneage of sea floor in m.y. mélange St. Helens 123 1 2463 597 Mount Adams WASHINGTON STATE GEOLOGY ? NORTH PACIFIC PLATE JUAN DE FUCA PLATE AMERICAN PLATE Washington is uniquely positioned for the study of the MANTLE geologic and structural setting of western North Amer- bouyant magma (mainly basalt) rises partial melting of subducting ocean crust forms magma ica. To the south in Oregon and Nevada, extensional to form new ocean crust (mainly andesite) that fuels Cascade Range volcanoes features predominate as reflected by basin-and-range terrain. To the east, the Rocky Mountains influence the Figure 2. A diagrammatic cross section through the Juan de Fuca spreading ridge and the Cascadia subduction zone (the area from the convergence zone geology of Idaho. To the north, western British Colum- east to where the Juan de Fuca plate sinks beneath the North American plate), bia is characterized by a massive coastal crystalline showing the magnetic orientation of the sea floor recorded at the Juan de Fuca belt and remnants of the geologic continent Wrangel- spreading ridge. Darker stripes in the cross section of the sea floor indicate times lia. All of these major crustal features of the adjacent when rock was created with a magnetic orientation of north. Notice that the age of regions terminate in or near Washington. The state’s the ocean floor is progressively older with distance from the spreading zone. The uniqueness is further enhanced by three major geologic pattern of ages approximately parallels the ridge on both sides. Mélange is a jum- bled mixture of continental shelf blocks and oceanic sediments that is faulted and conditions. First, Washington is impacted by crustal sheared at shallow depths in the subduction zone. Fore-arc folds and faults occur tectonics as the oceanic Juan de Fuca plate is being in a zone of crustal deformation between the subducting sea floor and the volcanic subducted under the North American continent (Fig. arc. Redrawn from Foxworthy and Hill (1982), Uyeda (1978), and Pringle (2002). 2). Second, the Columbia Basin (Fig. 3) in Washington and adjacent Oregon was subjected to great outpour- ings of basalt. Third, alpine and continental glaciation and glacial floods have created spectacular landforms OKANOGAN HIGHLANDS in the North Cascades, Puget Sound, and the Chan- NORTH WEST EAST neled Scablands. Washington’s geology is highly diverse. Rocks of OLYMPIC Precambrian age, as well as units from every geologic MOUNTAINS Seattle period, Cambrian to Quaternary, are represented. The Spokane PUGET state has been subject to continental collisions, meta- LOWLAND morphism, intrusion of igneous rocks, volcanism, COLUMBIA BASIN PALOUSE mountain-building episodes, erosion, glaciation, and SLOPE WILLAPA Pullman massive flooding events. This diversity has a strong in- HILLS YAKIMA fluence on soil productivity, location of mineral depos- FOLD BELT CASCADE RANGE Lewiston its, scenic grandeur, and even the climate. (Modified from the USGS/Cascades Volcano Observatory web- SOUTH BLUE site at http://vulcan.wr.usgs.gov.) PORTLAND MOUNTAINS BASIN 0 50 100 mi The Columbia River Portland 0 50 100 150 km Figure 3. The physiographic provinces and subprovinces of Washington State. The Columbia River pours more water into the Pacific Subprovinces are separated by a dashed line. The Columbia River Basalt Group Ocean than any other river in North or South America. underlies the Columbia Basin, part of the Portland Basin, and part of the Willapa In its 1270-mi (2045-km) course to the Pacific Ocean, Hills, as well as adjacent areas of Oregon and Idaho. 1 2 OPEN FILE REPORT 2004-7 49° CANADA 117 o 125° USA Mount CORDILLERAN ICE SHEET Baker CANADA River USA MONTANA Glacier Columbia Peak Columbia R. Everett ICE OLYMPIC Grand DAM Coulee ROCKYClark MOUNTAINS Dam MOUNTAINS Spokane R. Fork CASCADE SEATTLE SPOKANE R. River Wenatchee MISSION RANGE Glacial Lake Perma TACOMA Moses Spokane Lake PACIFIC OCEAN Olympia CHANNELED Glacial Lake Missoula Mount Columbia SCABLANDS Missoula Rainier Priest Rapids Pullman Dam Drummond River River IDAHO Yakima River PASCO Cowlitz Yakima BASIN Clearwater Lewiston River Richland Pasco Snake River Mount Kennewick Columbia St. Helens Mount Adams Darby Wallula Gap Walla Walla 46o BITTERROOT RANGE McNary River Dam Skamania Lodge The Dalles Dam Hood River Columbia PORTLAND John Day Bonneville Dam Dam RANGE The Dalles Troutdale Larch Mountain Highland Butte Mount Hood River OREGON EXPLANATION Mount Jefferson Snake Columbia River Basalt Group Area scoured by Missoula floods Glacial Lakes 0204060mi Ice-covered Lakes Figure 4. The probable extent of the Cordilleran ice sheet, ice-dammed glacial lakes, Missoula floods, and Columbia River Basalt Group. The failure of the ice dam of the Clark Fork River in western Montana released a 2000 ft (600 m) wall of water that rushed across eastern Washington again and again, eroding a series of intertwining canyonscalledcoulees.Thisareaisknownas the Channeled Scablands. The various flood pathways converged in the Pasco Basin, where there was a narrow exit for the waters—Wallula Gap. The narrowness of the gap caused the flood- waters to back up and form a 1200-ft (365-m)-deep lake covering over 3500 mi2 (9000 km2). Several other temporary lakes were created by similar events near The Dalles and Portland, Ore. (Modified from Waitt, 1985, and Weis and Newman, 1989. Extent of the Columbia River Basalt Group from Reidel and others, 1994.) GEOLOGY OF THE COLUMBIA RIVER GORGE, OREGON AND WASHINGTON 3 the Columbia flows through four moun- tain ranges—the Rockies, Selkirks, Cas- cades, and coastal mountains—and drains 258,000 mi2 (670,000 km2). The main stem of the Columbia rises in Co- lumbia Lake on the west slope of the Rocky Mountains in Canada. Its largest tributary, the Snake River, travels 1038 mi (1670 km) from its source in Yellow- stone National Park in Wyoming before joining the Columbia. The Columbia River Gorge is a spec- tacular canyon cutting through the Cas- cade Range.