Sentinel Gap

File:Sentinel-Gap-from-north-1.JPG

File:Sentinel Gap Ice Age Floods Features.webm

Sentinel Gap is a water gap formed by the Columbia River in the Saddle Mountains, near Mattawa in Washington state.{{GNIS|1508220|Sentinel Gap}} 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".{{sfn|Bjornstad|2006|p=242}} During Ice Age floods in which waters from the Channeled Scablands found passage to the Pacific Ocean here and at Wallula Gap,{{sfn|Soehnichsen|2012|pp=154-155}} this opening was "repeatedly reamed out, which probably widened and steepened the walls of the gap".{{sfn|Bjornstad|2006|p=242}} Strandlines from the floods can be seen on the basalt walls of the gap.{{sfn|Bjornstad|2006|p=92}}{{citation|title=Sentinel Gap and Mattawa Bar|date=November 7, 2009|author=Tom Foster|website=Ice Age Floods: Glacial Lake Missoula, Lake Bonneville and the Ice Age Floods|url=http://iceagefloods.blogspot.com/2009/10/sentinel-gap-and-mattawa-bar.html}}

SR 243 runs along the east side of the river through the gap, and the river is spanned by the Beverly Railroad Bridge.{{cite news |last=Lindsey |first=Kevin |date=July 25, 1983 |title=Columbia's early course visible at Sentinel Gap |page=D6 |work=Tri-City Herald}} 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 {{convert|4|miles}} downstream from Sentinel Gap.