The topographic basin of Davis Lake covers about 98 square miles and ranges in altitude from 4,390 feet at the lake to 8,744 feet at the summit of Diamond Peak. The lake is in volcanic terrane, which is marked by many cinder cones scattered on a lava plateau that slopes gently to the northeast. A surface deposit of highly permeable pumice overlies all but the most recent volcanic deposits and supports an almost continuous forest cover, chiefly of western yellow pine. Rainfall and melting snow readily infiltrate the highly permeable pumice cover and volcanic deposits. There is no information on the altitude and slopes of ground-water bodies, and the hydrologic boundary of the basin may not be the same as its topographic boundary.
Davis Lake occupies a channel that was slightly incised by Odell Creek into the surf ace of a lava plateau and was later filled downstream from the lake by a lava flow several hundred feet thick (fig. 8). The lava obstruction ponded the water and formed Davis Lake. Because Odell Creek seldom carries a significant load of sediment, the lake basin has not since been materially altered by sedimentary deposition, and the lava that forms the obstruction is not covered or sealed by sediment above the low-water level of the lake.
The lava flow is one of the youngest in the Cascade Range, and may be only about a thousand years old (Williams, 1953, p. 50-51). At places where windblown soil has collected between the blocks of lava, yellow pine trees grow, and some of them are probably at least 500 years old. The flow is not covered by the regional blanket of pumice from Mount Mazama (age, about 6,600 yr). Therefore, the basin apparently is at least 1,000 years but less than 6,600 years old. Davis Lake undoubtedly formed within a few months after the lava flow dammed the channel of Odell Creek.
Downstream from Davis Lake and the lava flow, the stream is called Davis Creek and is fed by large springs whose openings range from 4,310 to 4,360 feet in altitude. Some of the springs flow into Davis Creek channel just downstream from the lava flow, and others discharge within a mile downstream. Almost every year since Wickiup Dam was completed in 1949 at a site on the Deschutes River 10 miles northeast of Davis Lake, some of the springs have been submerged at times to a depth of about 25 feet by the water in Wickiup Reservoir. The topographic drainage area above the springs is 146 square miles, 46 percent more than that above Davis Lake.
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