Umtanum Ridge Water Gap

Umtanum Ridge Water Gap is a water gap cut by the Yakima River through Manastash and Umtanum Ridge anticlines, which are part of the Yakima Fold Belt near the western edge of the Columbia River Plateau located in central Washington state. This National Natural Landmark is characterized by a series of steep-sided ridges in the Columbia River basalt which are cut through by cross axially by the Yakima River. It is located also referred to as the Yakima River Canyon, and is located between the cities of Ellensburg and Yakima; State Route 821, originally the main route between Ellensburg and Yakima, parallels the river through the canyon.Babcock (2000)] Pub:Benchmark (2002)]

Geologic history

The great basalt flows of the Columbia Basin and of the Ellensburg Formation, in some places over 5000 meters (17,000 feet) thick, have been folded into ridges (anticlines) and valleys (synclines) running roughly east-west as at result of north-south compression. On its way to join the Columbia River, the Yakima River cuts from the Kittitas Valley southward through four major ridges formed by this compression: the Manastash Ridge, the Umtanum Ridge, the Yakima Ridge, and the Ahtanum Ridge to reach the Yakima Valley.

The highest ridge through which the Yakima flows, the Umtanum Ridge, rises to 983 meters (3225 feet) within 1 km of the river, which lies at about 470 meters (1540 feet) in elevation at the closest point. This unusual juxtaposition (rivers cutting through ridges rather than flowing through apparently more favorable routes) is an example of geologic precedence. The ancestral Yakima River is believed to have been there, flowing southward above the relatively flat basalt layers. As the layers compressed, the anticlines slowly rose. The river continued to follow its historic course, cutting downward through the basalt to maintain a relatively level. This view is supported by the significant meanders found in the canyon today; when a river has meanders, they tend to be preserved in rock as the river eats into a rising anticline.

Locations

References

Literature

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*cite book|author=Bjornstad, Bruce|title=On the Trail of the Ice Age Floods: A Geological Guide to the Mid-Columbia Basin |publisher=Keokee Books; San Point, Idaho |year=2006|id=ISBN 0-89886-548-4
*cite book|first=J Harlen|last=Bretz|id=ISBN |location= |title=The Channeled Scabland of the Columbia Plateau.|year=1923|publisher= "Journal of Geology", v.31, p.617-649
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*cite book|first=Ted and Marge|last=Mueller|id=ISBN 0-89301-206-8|location= |title=Fire, Faults & Floods|year=1997|publisher=University of Idaho Press, Moscow, Idaho
*cite book|first=|last=|id=ISBN |location= |title=Channeled Scabland of Eastern Washington:The Geologic Story of the Spokane Flood|year=1982|publisher=U.S. Government Printing Office, Washington D.C.
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