Half Dome is a granite dome at the eastern end of Yosemite Valley in Yosemite National Park, California. It is a well-known rock formation in the park, named for its distinct shape. One side is a sheer face while the other three sides are smooth and round, making it appear like a dome cut in half. The granite crest rises more than 4,737 ft (1,444 m) above the valley floor. The impression from the valley floor that this is a round dome that has lost its northwest half is an illusion. From Washburn Point, Half Dome can be seen as a thin ridge of rock, an arête, that is oriented northeast-southwest, with its southeast side almost as steep as its northwest side except for the very top. Although the trend of this ridge, as well as that of Tenaya Canyon, is probably controlled by master joints, 80 percent of the northwest "half" of the original dome may well still be there. On March 28, 2009, a large rock slide of 1,500,000 cubic feet (42,000 m3) occurred from Ahwiyah Point. The slide happened at 5:26 a.m. and damaged a large area under the dome. No one was injured, but hundreds of trees were knocked down, and a portion of the Mirror Lake trail was buried. The slide registered on seismographs as an earthquake reaching 2.5 on the Richter Scale. As late as the 1870s, Half Dome was described as "perfectly inaccessible" by Josiah Whitney of the California Geological Survey.[6] The summit was finally conquered by George G. Anderson in October 1875, via a route constructed by drilling and placing iron eyebolts into the smooth granite. Today, Half Dome may now be ascended in several different ways. Thousands of hikers reach the top each year by following an 8.5 mi (13.7 km) trail from the valley floor. After a rigorous 2 mi (3.2 km) approach, including several hundred feet of granite stairs, the final pitch up the peak's steep but somewhat rounded east face is ascended with the aid of a pair of post-mounted braided steel cables originally constructed close to the Anderson route in 1919. Alternatively, over a dozen rock climbing routes lead from the valley up Half Dome's vertical northwest face. The first technical ascent was in 1957 via a route pioneered by Royal Robbins, Mike Sherrick, and Jerry Gallwas, today known as the Regular Northwest Face. Their five-day epic was the first Grade VI climb in the United States.Their route has now been free soloed several times in a few hours' time. Other technical routes ascend the south face and the west shoulder. The Half Dome Cable Route hike runs from the valley floor to the top of the dome in 8.2 mi (13 km) (via the Mist Trail), with 4,800 ft (1,460 m) of elevation gain. The length and difficulty of the trail used to keep it less crowded than other park trails, but in recent years the trail traffic has grown to as many as 800 people a day. The hike can be done from the valley floor in a single long day, but many people break it up by camping overnight in Little Yosemite Valley. The trail climbs past Vernal and Nevada Falls, then continues into Little Yosemite Valley, then north to the base of the northeast ridge of Half Dome itself. The final 400 ft (120 m) ascent is steeply up the rock between two steel cables used as handholds. The cables are fixed with bolts in the rock and raised onto a series of metal poles in late May (the poles do not anchor the cables). The cables are taken down from the poles for the winter in early October, but they are still fixed to the rock surface and can be used. The National Park Service recommends against climbing the route when the cables are down and when the surface of the rock is wet and slippery. The Cable Route is rated class 3, while the same face away from the cables is rated class 5. The Cable Route gets crowded on the weekends The Cable Route can be crowded. In past years, as many as 1,000 hikers per day have sometimes climbed the dome on a summer weekend, and about 50,000 hikers climb it every year.

• published: 14 Apr 2016
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