Boundary) are its principal tributaries from the E.; the Yakima (a little above the mouth of the Snake) from the W.; and the Okanogan (in the north central part of the state), from the N.
Along the coast the prevailing winds blow from the west or south; in the Puget Sound Basin from the south, and in eastern Washington from the south-west, except in the Yakima and Wenatchee valleys, where they are north-west.
The Yakima project involved the irrigation of about 600,000 acres by means of five reservoirs of an aggregate area of 804,000 acre-feet, and was undertaken by the United States government in 1905.
Part of the state much alfalfa is grown, especially in Yakima county.
The Northern Pacific, the first of the transcontinental roads to touch the Pacific north of San Francisco, reaches Seattle with a wide sweep to the south, crossing the Columbia river about where it is entered by the Yakima and ascending the valley of the latter to the Cascade Mountains.
Part of the state, and the Yakima Reservation (837,753 acres unallotted), in the S.
In a few localities, notably in South Dakota, the Yakima valley of Washington, San Joaquin, and San Bernardino valleys of California, San Luis valley of Colorado, and Utah valley of Utah, water from artesian wells was also used for the irrigation of from 1 to 160 acres.