cones in the Boring Lava Field. During the Pliocene (5 million to 2 million years ago), hyaloclastite formed from interaction of Cascade, alumina-rich basalt lava with the Columbia River. After these hyaloclastite units were deposited, further deformation occurred, leading to the accumulation of gravel and lithic fragments to elevations of in the Portland area. Powell Butte is partially mantled by post hyaloclastite gravel from the Troutdale Formation, which is likely the result of redeposited soil after erosion. Like the rest of the Boring Lava Field, Powell Butte is extinct. Climate and ecology The climate at Powell Butte is cool, creating a short growing season environment. It supports grass meadows, which sustain apple, pear, and walnut trees. Powell Butte sits near Johnson Creek, a tributary of the Willamette River that sustains native salmon and rainbow trout. It also supports the Powell Butte Nature Park and its associated meadow and forest areas. These habitats are populated by bats, black-tailed mule deer, chipmunks, coyotes, gray foxes, ground squirrels, rabbits, raccoons, ring-necked pheasants, and skunks. Birds of prey are common among the park's open meadows, groves of wild hawthorn and western red cedar trees, and wetlands. Kestrels and red-tailed hawks hunt on top of the butte. There are mixed forests of bigleaf maple and Douglas fir trees on the butte's northern side. Human history Powell Butte lies within historic territory of the Confederated Tribes of the Grand Ronde Community of Oregon, which covered more than and extended from the Columbia River to the Klamath River. At the end of the 19th century, much of the meadow area near Powell Butte was cleared and replaced with an orchard by settlers. In 1925, the Portland city government bought the land encompassing Powell Butte from George Wilson with the intent to use it for water reservoirs. They leased the northeastern part of the land to farmer Henry Anderegg, who owned and operated the Meadowland Crest Dairy until 1948. In the mid-1970s, Portland's Water Bureau created a development plan for Powell Butte including four underground reservoirs to be built at the northern side of the mountain. The first of these reservoirs was constructed in 1981 and the second in 2014. Recreation Powell Butte hosts the Powell Butte Nature Park, which encompasses an area of about . The nature park was established by Portland city government in 1987 and opened to the public in 1990 and is maintained by