flows is clearly visible in the folded layers of basalt exposed in the steep walls of the gap.

Creation of the Wallula Gap

Early in the history of folding, the ridge crest at Wallula Gap must have been the lowest along the ridge. The ancient Salmon-Clearwater River began to flow across the ridge over this low point, cutting a channel. As the ridge continued to fold upward, erosion cut through and the water gap was formed.

Until about ten million years ago, the Salmon-Clearwater River flowed through the Wallula Gap alone.

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