Sentinel Gap is a water gap formed by the Columbia River in the Saddle Mountains, near Mattawa in Washington state. [1] The gap is "a water gap where erosion by the Columbia River was able to keep pace with folding, faulting and uplifting across the Saddle Mountain anticline". [2] During Ice Age floods in which waters from the Channeled Scablands found passage to the Pacific Ocean here and at Wallula Gap, [3] this opening was "repeatedly reamed out, which probably widened and steepened the walls of the gap". [2] Strandlines from the floods can be seen on the basalt walls of the gap. [4] [5]
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SR 243 runs along the east side of the river through the gap, and the river is spanned by the Beverly Railroad Bridge. [6] The gap is located between the Wanapum and Priest Rapids dams. Priest Rapids, for which the dam was named, are now submerged beneath the dam's reservoir about 4 miles (6.4 km) downstream from Sentinel Gap.
