Sentinel Gap

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]

Sentinel Gap

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.

References
  1. U.S. Geological Survey Geographic Names Information System: Sentinel Gap
  2. Bjornstad 2006, p. 242.
  3. Soehnichsen 2012, pp. 154-155.
  4. Bjornstad 2006, p. 92.
  5. Tom Foster (November 7, 2009), "Sentinel Gap and Mattawa Bar", Ice Age Floods: Glacial Lake Missoula, Lake Bonneville and the Ice Age Floods
  6. Lindsey, Kevin (July 25, 1983). "Columbia's early course visible at Sentinel Gap". Tri-City Herald. p. D6.

Sources
  • Bjornstad, Bruce N. (2006), On the Trail of the Ice Age Floods: A Geological Field Guide to the Mid-Columbia Basin, Keokee Books, ISBN 9781879628274, OCLC 70697754
  • Soehnichsen, John (2012), Washington's Channeled Scablands Guide, The Mountaineers Books, ISBN 978-1-59485-483-5, OCLC 910880058

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