soil derived from Mazama Ash (ash erupted from Mount Mazama). Stream flow changes little throughout the year due to the region's volcanic hydrogeology. These slopes support nearly pure stands of ponderosa pine. Understory vegetation includes greenleaf manzanita and snowberry at higher elevations and antelope bitterbrush at lower elevations. Mountain alder, stream dogwood, willows, and sedges grow along streams. Local fauna includes birds such as blue and ruffed grouse, small mammals like pikas, chipmunks, and golden-mantled ground squirrels, and larger species like the Columbian black-tailed deer, mule deer, Roosevelt elk, and American black bear. Bobcats, cougars, coyotes, wolverines, martens, badgers, weasels, bald eagles, and several hawk species are many of the predators throughout the Three Sisters area. Human history The Three Sisters area was occupied by Amerindians since the end of the last glaciation, mainly the Northern Paiute to the east and Molala to the west. They harvested berries, made baskets, hunted, and made obsidian arrowheads and spears. Traces of rock art can be seen at Devils Hill, south of South Sister. The first Westerner to discover the Three Sisters was the explorer Peter Skene Ogden of the Hudson Bay Company in 1825. He describes "a number of high mountains" south of Mount Hood. Ten months later in 1826, the botanist David Douglas reported snow-covered peaks visible from the Willamette Valley. As the Willamette Valley was gradually colonized in the 1840s, Euro-Americans approached the summits from the west and probably named them individually at that time. Explorers, such as Nathaniel Jarvis Wyeth in 1839 and John Frémont in 1843, used the Three Sisters as a landmark from the east. The area was further explored by John Strong Newberry in 1855 as part of the Pacific Railroad Surveys. In 1862, to connect the Willamette Valley to the ranches of Central Oregon and the gold mines of eastern Oregon and Idaho, Felix and Marion Scott traced a route over Scott Pass. This route was known as the Scott Trail, but was superseded in the early 20th century by the McKenzie Pass Road further north. Around 1866, there were reports that one of the Three Sisters emitted some fire and smoke. In the late 19th century, there was extensive wool production in eastern Oregon. Shepherds led their herds of 1,500 to 2,500 sheep to the Three Sisters. They arrived in eastern foothills near Whychus Creek by May or June, and then climbed to higher