Tuesday, November 15, 2011

Mini Badland Southeast of Bridgeport

Highway 174 from Grand Coulee to Bridgeport takes one up onto the northeast part of the Watterville Plateau and glacier scoured landscapes. The road then drops down into the East Foster Creek drainage and follows the drainage back down to the Columbia River to Bridgeport and Chief Joseph Dam. This valley has some mini badlands. Bare white/gray silt bluffs are scattered along the valley like old dump piles of soil, and the same silts area exposed along steep cut bank slopes adjacent to the creek.

Level terraces along the valley sides provide a clue as to the origin of the silt that makes up the bad land. Once the Okanogan ice lobe retreated back off the Watterville Plateau it still dammed the Columbia River creating a lake that extended up stream and up the valley the road passes down. That lake was filled with silt from finely ground rock from the glacial ice. The fine silts settled on the lake bed as a thick blanket of silt. Subsequent erosion has left a mini bad land and the terraces in the East Foster Creek drainage. The soil properties of the silt are somehow not conducive to plant cover at least in this local climate.

Lake terrace is the level line bench on the valley slope.

The lake formed by the Okanogan ice lobe varied in size and depth depending on how far the ice extended to the south and how thick the ice was. Sediments from this glacial lake are a common feature all along the Columbia River valley upstream from Chief Joseph dam. As posted previously the lake also must have had some big ice bergs as some huge boulders are scattered within the lake sediments glacial-erratics-near-grand-coulee-dam. Another version of the lake played a key role in shaping and directing the Missoula Floods across eastern Washington as water from the lake spilled out of the valley south across the landscape.

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