by the Scottish blacksmith of Yosemite Valley, George C. Anderson. A rope that Anderson laid was used by six men, including 61-year-old Galen Clark, and one woman, to scale the last of Half Dome. Anderson's rope was repaired several times and was replaced in 1919 by a stairway built by the Sierra Club. Sunnyside walk-in campground, better known as Camp 4, was built in 1929. Rock climbers, who started to scale the cliffs of Yosemite in the 1950s, camped there. In 1997, a flood in Yosemite Valley destroyed employee housing in the valley. The Park Service wanted to build dormitories next to Camp 4, but Tom Frost, the American Alpine Club and others succeeded in killing the plan. Camp 4 was listed on the National Register of Historic Places on February 21, 2003, because of its role in the development of rock climbing as a sport. Badger Pass Ski Area was established in 1935. The 9-hole Wawona Golf Course opened in June 1918 in a meadow adjacent to the Wawona Hotel. A golf course was later built near the Ahwahnee Hotel in Yosemite Valley, but was removed and converted into a meadow in 1981. Introduced and invasive species Introduced animals and diseases had impacted the park area by the late 19th century. Galen Clark noted in the mid-1890s that native grasses and flowering plants in Yosemite Valley had been reduced in number by three-quarters. White pine blister rust, a fungal disease that infects conifer trees, was accidentally introduced in British Columbia in 1910 and had reached California by the 1920s. It has since infected many sugar pine trees in the Yosemite area. The rust is managed by removing plants belonging to the ribes genus, which act as carriers of the fungus. Trout were introduced in Yosemite streams and lakes to promote fishing. Tadpole predation by the introduced fish reduced frog populations. Lakes and streams are no longer stocked in the park. Current park managers focus on controlling nine high-priority invasive plant species of noxious weeds: yellow star-thistle (Centaurea solstitialis); spotted knapweed (Centaurea maculosa); Himalayan blackberry (Rubus armeniacus); bull thistle (Cirsium vulgare); velvet grass (Holcus lanatus); cheat grass (Bromus tectorum); French broom (Genista monspessulana); Italian thistle (Carduus pycnocephalus); and perennial pepperweed (Lepidium latifolium). In 2008, the park began to use the herbicides glyphosate and aminopyralid to augment manual methods to manage the most threatening plants. Wildlife Brown bears, also called grizzlies,