river, c.375 mi (600 km) long, rising in the De Long Mts. of the Brooks Range, NW Alaska, and flowing across the tundra, east then north, to the Arctic Ocean. All of its major tributaries rise on the north slope of the Brooks Range. The river, frozen for most of the year, floods each spring as ice on its upper course melts. Umiat is the chief village along its banks. Coal, oil, and natural gas are found in the valley.