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3 2: River context Climate The Kittitas Valley is located in the arid eastward side of the Cascade Mountains at an elevation about 3,170 feet above sea level. Mean temperatures vary from a high of 82 degrees in July to a low of 20 degrees Fahrenheit in January with extreme variations recorded at -3 to a high of 102 degrees Fahrenheit. Average annual precipitation is about 18 inches of rain and 65 inches of snow over 101 days with a mean growing season with temperatures above 32 degrees Fahrenheit for about 170-190 days. Approximately 80% of the precipitation occurs from October through March with less than 6% falling during June, July, and August. The valley receives about 201 sunny days per year making it a popular recreation area. Earth The Kittitas Valley is located within the western edge of the North Rocky Mountain System. The Cascade Mountains were created by continuous volcanic activity along the border of the underlying continental plates. The mountains were in turn, subject to the action of periodic glacial intrusions - the most recent being the Pleistocene glacial period more than 15,000 years ago. The Pleistocene glacial intrusion created a series of glacier dams in Missoula, Montana that subsequently breached and flooded the eastern portions of the state a number of times creating the Columbia River drainage channels. The Kittitas Valley is composed of a series of alluvial benches filled in by the Columbia River during the Missoula Floods. The benches are in turn bisected by a number of tributary drainage corridors created by the Columbia and Yakima Rivers. Over time, the rivers and tributary drainage streams created dramatic hillsides and overlooks, particularly of the Columbia River basin. Topography ranges from 600 feet in the lowest portion of the valley to about 8,000 feet above sea level in the Cascade Mountains. The plateaus and foothills overlooking the Kittitas Valley and the Yakima River in particular drop off abruptly in slopes ranging from 40% to 75%. Water Four rivers and a number of minor streams drain the Kittitas Valley: ¥ Yakima River – the longest river in Washington State, drains the eastern side of the Cascade Mountains beginning in Keechelus Lake, at an elevation of 2,449 feet and extending through Lake Easton, merging with the Cle Elum River, Teanaway River, Naches River, and eventually merging with the Columbia River in Richland. The river flows through Easton, Cle Elum, around Ellensburg and Yakima, and southeast to Richland, where it flows into the Columbia River at a distance of 214 miles, an elevation of 340 feet, and an average drop of 9.85 feet per mile. About 85 miles of the river is located in Kittitas County beginning at Keechelus Lake and ending at Roza Dam at the Yakima County line. Average daily streamflow varies from 648 cubic feet per second (cfs) below Keechelus Lake to 2,468 cfs at Thorp Bridge to 3,206 cfs in the Lower Canyon.