A major source of damage to the park in the late 19th century and early 20th century was summer livestock grazing, particularly sheep, in areas such as Tehipite Valley and the Roaring River valley (although sheep never entered Cedar Grove, due to the difficulty of accessing the bottom of Kings Canyon before Highway 180 was constructed). Ranchers drove their herds up into the Sierra Nevada to escape the drought and heat of the San Joaquin Valley. Meadows were trampled by thousands of hooves, leading to increased erosion and watershed degradation.: Grizzly bears and wolves which preyed on livestock were shot, trapped and poisoned in large numbers, extirpating them from the Sierra by the early 1900s.