Repeated Deformation along Lake Rufus Woods, WA

Lake Rufus Woods is a 50-mile long reservoir formed by Chief Joseph Dam. The reservoir extends from Bridgeport to Grand Coulee, WA. Access the lake by boat or via short hikes from Hwy 155/Columbia River Rd (Colville Indian Reservation land), or via gravel roads leading north from Hwy 174 (Strahl Canyon Rd). Excellent golfing can be had at nearby Gamble Sands, designed by David McClay Kidd and ranked #1 Best Course in Washington by Golf Magazine in 2021.

Geology exposed in shoreline bluffs along this remote reach of the Columbia River has received little attention over the past century, despite the miles of exposure and fairly easy access. Evidence of repeated Missoula flooding appears as sandy, deformed intervals sandwiched between flat-lying clay-silt varves of Glacial Lake Columbia, the "Nespelem Silt" of Pardee (1918). Deformed zones up to several meters thick resemble deformed zones in the Sanpoil Valley, Hawk Creek, Wilmont Creek, and Upper Columbia. Loading and mass wasting deformation is also common in the section. The Okanogan Lobe overrode the area. Till uplands above the canyon are littered with huge haystack boulders of basalt. The Columbia River Basalt onlaps older granitic rocks here.

A long profile analysis of a conspicuous flight of Pleistocene-age terraces has not been made, but would make a great student project: Is there an isostatic uplift signature preserved in terrace profiles along Rufus Woods Lake?

Photos below are from a 2019 visit I made to the China Creek/Alameda Flat area.

This pattern repeats in shoreline bluffs.

Surf's up.

Deformed sands.

Deformed varves (lakebeds).

Soft sediment deformation structures of various types are found wherever you look.

Interesting micro-faulting in sandy units at China Creek.

Sand-filled fracture forms a clastic dike.

The barn owl nests are also interesting. The wing-flap marks left by arriving owls are particularly cool.

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