Craton to Accreted Terranes: An Overview of Pacific Northwest Geology

Spring 2010 Regional Geology Field Trip May 2010
GEO 490/590 Forward

The following field trip guide was compiled and written by the student participants in the Department of Geological Sciences, University of Alabama Seminar in Regional Geology -- GEO 490/590 during Spring semester 2010. This trip was specifically designed in order to introduce the complex geology resulting from accretion of island arc and related mélange and sedimentary terranes to the western margin of North America. Therefore, the field trip stops span from the North American craton and Salmon River Suture Zone of western Idaho, the Blue Mountains Province of Northeastern Oregon and the North Cascades Crystalline Core to the High Cascades of Washington. The resulting guide is as complete and accurate as possible given the time constraints.


The Geology

The ‘Craton to Accreted Terranes: An Overview of Pacific Northwest Geology’ trip focused on six geologic features or regions in the Pacific Northwest of Idaho, Oregon, and Washington:

  1. Columbia River Basalts, Columbia River Gorge, WA and OR
  2. Western Idaho Shear and Salmon River Suture Zone, McCall to Riggins ID
  3. Blue Mountains Province: Wallowa and Baker terranes, Hells Canyon to Pilot Rock, OR
  4. Swakane Gneiss, Cascades Crystalline Core, Wenatchee to Entiat, WA
  5. Wenatchee Block, Cascades Crystalline Core, Leavenworth to Stevens Pass, WA
  6. Mount Saint Helens and the High Cascades


An Account of the Field Trip

The GEO 490/590 field trip began with an early morning flight from Birmingham, AL to Portland, Oregon. After an unpleasantly protracted effort to rent a van, the class drove up the Columbia River on Interstate 84 to Memaloose State Park where we spent our first night. On the first full day of the trip, we examined the stratigraphy and an anticline in the Columbia River Basalts from the Roweena Overlook, then drove east on Interstate 84 through Baker City, Oregon to Weiser, Idaho. In Weiser, we turned north on US 95 to New Meadows, then east on ID 55 to McCall. Our route to examine Precambrian rocks north of McCall was blocked by snow and the group instead looked at a Late Cretaceous phase of the Idaho Batholith. As night approached, we retraced our route on ID 55 to the appropriately named Last Chance campground in Payette National Forest where we spent a chilly night. On May 12, we drove north on US 95 to Riggins where we drove east along the Salmon River Road to examine metamorphic rocks in the Salmon River Suture zone. We camped on a sandy beach along the river, then spent the morning of May 13 sampling garnet schist near Riggins. After sampling, we drove south on US 95 and then west on ID 71 to Hells Canyon. After a picnic by the Snake River, we continued west to Sparta, OR where we had our first up close look at the southern Wallowa terrane of the Blue Mountains Province. We continued west to Baker City and examined additional imbricated Wallowa rocks faulted into the Baker terrane and then enjoyed the hospitality of Mark Ferns, who provided much appreciated space for us to sleep at his house. On May 14, we drove west on Interstate 84 and OR 244, north on US 395 to Battle Mountain, OR where we examined deeply weathered Late Jurasic plutonic rocks of the Mountain Home Metamorphic complex. We then drove to Pilot Rock, Oregon and continued south on Yellow Jacket Road where we spent several hours examining garnet-biotite schists.. After sampling garnet schists, we drove north to Interstate 90, west to George Washington, and then north on US 97 to Daroga State Park where we spent a pleasant night on the Columbia River. May 15 and 16 were spent exploring outcrops of the Swakane Gneiss along the Columbia River and in Roaring Canyon. On the night of May 15th we camped at Fox Creek campground (Wenatchee National Forest) on the Entiat River. On the afternoon of May 16, we drove west on US 2 to Leavenworth and camped at Eightmile campground (Wenatchee National Forest) in Icicle Canyon. On May 17, we examined outcrops of the Chiwaukum Schist, Nason Ridge Migmatitic Gneiss, and Mount Stuart batholith. That night, we camped at Nason Creek Campground (Wenatchee National Forest) near Lake Wenatchee. The following day May 18th, we drove north on the White River Road to look at the Tenpeak Pluton, then drove back to Leavenworth, south on US 97 to Yakima, and then west on US 12 to Taidnapam Park on Riffe Lake. We camped at the park and then on May 19th drove west to Interstate 5, south on the interstate to Woodlawn, Washington, and then east to Mount Saint Helens on WA 503. After lunch, we caught glimpses of the volcano from the road and then walked the length of Ape Cave lava tube. With this adventure, the field trip ended and the group returned to Portland for the flight back to Tuscaloosa.


Participants
The following faculty and students participated in the 11-day trip, May 10-20, 2010:
Alexander, Ryan S.
Anderson, Bryan S.
Gatewood, Matthew P.
Gentry, Natalie E.
Hollon, Brittany E.
Holmes, Whitney B.
McKay, Matthew P.
Rutter, Rachael S.
Schwartz, Joshua J.
Shields, Rebecca F.
Stowell, Harold H.
Wilson, Kevin L.

Acknowledgments
We gratefully acknowledge financial assistance from the University of Alabama Department of Geological Sciences, NSF Grants EAR 0710922 & 0911681, and the University of Alabama Graduate Student Association. Sandra Stowell and Mark and Betsy Ferns are thanked for providing camping gear and sleeping space, respectively.


Snow Battle for US-2 Turn Around