COLUMBIA RIVER, the largest river flowing into the Pacific from the western continent, rises in the ice fields of the Rocky mountains in British Columbia (5o° N., 116° W.), about 8o m. N. of the international boundary. It flows northwest for about 17o m. to lat. 52°, where it turns sharply south nearly encircling the Selkirk mountains; next, through a series of narrow lakes, it enters the United States near the northeast corner of Washington. Just before crossing the frontier it is joined by Clark Fork. Through Washington the Columbia flows circuitously, in what is called the Big Bend, to its junction with the Snake, its largest tributary, not far below which it turns west and forms the bound ary between Washington and Oregon for about 325 miles. The ice of the Glacial period, which extended as far south as the Big Bend, greatly modified its course which was once the line of the series of lakes in the Grand Coulee. Below its confluence with Clark Fork the Columbia receives, besides the Snake, the Spo kane, Okanogan, Wenatchee, Yakima, Walla Walla, Umatilla. John Day, Deschutes and Willamette rivers. The total area drained by this system is 259,000 sq.m., of which 220,3oo are in the United States. The total length of the river is about z,400 miles. Its mean flow at its mouth is about 28o,000 second feet (maximum about 1,250,000) and at the Danes is 2o5,000 second feet. This is about eight times the mean flow of the Colorado at Yuma, and nearly double that of the Nile at Assuan.
The fall through 400 m. in Washington is over i,000 ft., and its water power and that of its tributaries (over o,000,000 h.p.), is now a subject of study by Government and other engineers, for irrigation as well as flood control purposes. Less than 7oo,000 h.p. is utilized in the United States. About 3,600,000 ac. are irrigated from its system and it is believed that 4,400,000 ac. can be added.
Almost everywhere down to the mouth of the Snake the Colum bia is cutting down its bed and below the Spokane flows through a very steep and rugged canyon. From the mouth of the Okano gan to Priest rapids (14o m.) the walls are of black basalt rising in places i,000 to 3,000 ft. above the river. The finest part of this canyon lies below Rock Island rapids.
The mouth of the Columbia is the only deep-water harbour be tween San Francisco and Cape Flattery, a distance of 77o miles. The tides are perceptible 130 m. up the river. The mean tide at Astoria is about 6 feet. The average tidal flow at the mouth is about i,000,000 second feet. With the completion of the locks at Stevenson, the river is navigable by sea-going vessels as far as The Dalles, 206 miles from the mouth. In 1926 1,760 sea-going vessels passed in and out, carrying 6,296,879 tons of freight, valued at $315,139,879. Improvements at the bar at the mouth of the Columbia have been made by the Government, and on the Willamette, below Portland, by the Government in co-operation with the municipal Port of Portland. A project for a 3o ft. channel, 3oo ft. wide, from Portland to the sea was authorized in 1911, and a channel of those dimensions has been maintained by dredging and by the construction of permeable spur dikes. A 35 ft. channel, 5oo ft. wide, was authorized in 1928. At the bar at the mouth of the Columbia a depth of 46 ft. at low water for a width of 3,2oo ft. is now available. The total cost of the jetties and the dredging at the mouth of the river up to June 3o, 1927, was $14,230,737, and that of similar work below Portland, on the Willamette and the Columbia up to the same date was $10,223,343. Steamboat navigation was formerly obstructed by the Cascades, which begin about 14i m. from the ocean, at a point where the river passes the main divide of the Cascade range. Here it flows in a narrow, steep-sided gorge, around which a canal 3,000 ft. long has been built. About so m. above the Cascades the Dalles Celilo canal enables steamboats to pass around similar rapids.
The salmon fisheries on the Columbia and its tributaries sup ply large canneries, with an an nual output of $4,000,000. The Government maintains large sal mon hatcheries on several streams and releases millions of young salmon annually.
Possibly in 1788, and certainly in 1792, the mouth of the Columbia was entered by Captain Robert Gray of Boston, Mass., who changed its earlier name, "Oregon," to Columbia. In 1804— '805 the river was explored by Lewis and Clark, upon whose discoveries the United States primarily based its claim to what now comprises Oregon and Washington. (G. McL. Wo.) COLUMBIA RIVER HIGHWAY begins at Astoria, Ore gon, and ends at Pendleton, 336m. distant in the same State. Of this mileage 202M. dre paved and 134m. are of oiled rock or gravel. It runs within sight of the Columbia river practically all the way, sometimes along its lower banks and sometimes along rocky walls at great heights above the stream, often passing by tunnel through projecting mountain spurs. Portland, Hood River, The Dalles and Umatilla and also the great snow-crowned peaks, Multnomah Falls and Mt. Hood are points of interest along its course. It is part of the old "Oregon Trail" made famous by the Astor family and is one of the most notable scenic highways in America.