Tuesday, October 4, 2011

McBee Road Landslide

Ancient landslide south of Kiona and Benton City
McBee Road traverses across the slide

There are a fair number of large ancient landslides on the north facing slopes of the folds in the Yakima Fold Belt. The folds are generally very asymmetric with very steep north slopes and gentle south slopes. The folds are tight enough on the steep north slopes to have highly fractured the basalt bedrock of the Columbia River Basalt Group and in some areas minor thrust faults are present. The above picture was taken in the morning from the road that crosses the south slope of Red Mountain - a hot spot vineyard area. I had been on McBee Road earlier in the morning and had observed the landslide from the side.

Side view of landslide at McBee Road

A coherent slide block with a classic back slope towards the slide area can be seen on the right along with the classic lumpy terrain on the slide area compared to the smooth plainer slopes with valleys between me and the landslide. Many of the slides may have been triggered by the lower sloes getting saturated and/or eroded by the flood waters from the Missoula floods.

The bunch grass also stood out very well in the early morning light. The land is managed by the Bureau of Land Management. The steepness and dry conditions apparently never appealed to any homesteaders or the railroad land men leaving this land area in public ownership.

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