and extending east of the Cascades almost to the Idaho boundary, is the Columbia Basin, an area approximately 1,500,000 acres of sage and scabland. From an elevation of 500 feet at the Columbia River, lowest point in the region, the basin rises rapidly westward toward the foothills of the Cascades; eastward, the rise is more gradual to an elevation of approximately 2,000 feet at the Idaho Line. Ridges, extending east and west through the basin and marking the eroded course of past ice sheets, once rose across streams, but the latter in time have cut through them. The area of the Big Bend is scarred by great, ancient, long-dry river courses, of which Moses Coulee and Grand Coulee are excellent examples. Some of the coulees, however, still hold chains of lakes, strongly alkaline. From the region of the deep canyons of the Snake River and its tributaries, rolling plateaus—the Palouse Country —extend north and east, a fertile region of wind-borne soil deposits.
In the southeastern corner of the State are the Blue Mountains, a prominent uplift of some 7,000 feet in the lava plain. The rounded domes, rising 2,000 to 4,000 feet above the surrounding basin lands, receive, in contrast to the contiguous country, enough rainfall to support forest growth. The streams, in deep valleys, have affected general contours very little.
CLIMATE
Washington's topography, together with warm sea currents, strongly affects the climate, which varies greatly in different areas. Rainfall ranges from extremes of 6 inches in the eastern part to 16 inches in the western. East of the Cascades summer temperatures are often above 100° F. Not uncommonly, eastern Washington winters drop to —20⁰ F. and —30° F., and crop seasons in the northern and higher portions are sometimes less than 100 days, increasing to 200 days towards the south. The average annual precipitation of 16½ inches in this section ranges from 60 inches in the mountains to 6 inches on the plains. The westerly prevailing wind's average velocity is low—between 5 and 6 miles per hour—but occasional sand or dust storms visit the arid areas.
In western Washington, the heaviest rainfall in the United States occurs on the southwestern slope of the Olympics, at Wynonche, where the average is 141 inches. On the northern side of the Olympics, Sequim has the lightest rainfall, averaging 17 inches, and requires irrigation. The average in the western section, however, 36 inches. The rainiest month is likely to be December, and the driest, July. Winter temperatures average 40° F., with a daily average minimum of 35%. Summers
