East of the Cascade Mountains the Columbia and Spokane rivers mark the boundary between the Okanogan Highlands to the northward and the Columbia plateau to the southward; The Okanogan Highlands, an outlier of the Rocky Mountains extending westward from the Coeur d'Alene Mountains in Idaho, reach heights of 5000 to 6000 ft.
The Okanogan Highlands, the Columbia plain, the E.
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.
Slope of the Cascades and most of the Okanogan Highlands are clothed with light forests consisting chiefly of yellow pine, but containing also Douglas fir, cedar, larch, tamarack and a very small amount of oak.
In the eastern part of the Okanogan Highlands there is some western white pine, and here, too, larch is most abundant.
On the Okanogan Highlands, on the eastern foothills of the Cascade Mountains, on the Blue Mountains and on the elevated portion of the Columbia Plain which comprises the E.
Slope of the Cascades and on the Okanogan Highlands glacial deposits of clay, gravel or sand, as well as vegetable loam, are mixed with the volcanic substances.
The principal Federal irrigation undertakings in 1910 were known as the " Okanogan project " and the " Yakima project."
The former (authorized in 1905) provided for the irrigation of about 10,000 acres in Okanogan county by means of two reservoirs of an aggregate area of 650 acres, main canals and main laterals 20 m.
The largest output of each of these ores in 1908 was in Stevens county; Ferry, King and Okanogan counties ranked next in the output of gold; Okanogan and Ferry counties in the output of silver; Okanogan in the output of copper; and King in the output of lead.
In 1811 the Pacific Fur Company, a kind of western division of the American Fur Company, founded a trading post at the mouth of the Columbia which they called Astoria, and set up a number of minor posts on the Willamette, Spokane and Okanogan rivers.
Tungsten is found as wolframite in Stevens county near Deer Trail and Bissell, in Okanogan county near Loomis, in Whatcom county near the international boundary, and (with some scheelite) at Silver Hill, near Spokane.