Umatilla ŭm˝ətĭl´ə [key], river, c.85 mi (140 km) long, rising in NE Oreg. in the Blue Mts. It flows W past Pendleton, then NW to the Columbia River at the city of Umatilla (1990 pop. 3,046). The Umatilla project taps two of the river's tributaries for irrigation.

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