California wildfire heads deeper into Yosemite, entry road closed SAN FRANCISCO (Reuters) - Yosemite National Park, faced with the spread of a massive California wildfire, closed a second key route into the park on Wednesday that could keep some visitors from reaching one of the nation's top outdoor destinations over the Labor Day weekend. The shutdown of Tioga Road comes as the so-called Rim Fire, which has now scorched an area larger than the land mass of Chicago, was burning deeper into the park and headed toward the tourist hub of Yosemite Valley. The blaze, which stands as the sixth largest on record in state history, on Tuesday reached a reservoir that serves as the primary water supply for San Francisco, some 200 miles to the west. Crews were attacking the eastern flank of the fire as it spread toward Yosemite Valley as well as the western edge, where some 4,500 homes in a string of small communities stood in the path of the flames, California Department of Forestry and Fire Protection spokesman Dennis Matheson said. He said that treacherous, often inaccessible terrain was largely preventing firefighters from cutting new lines around the blaze and estimated it would take another week to fully contain it. "I think it's very safe to say that we're looking at least at the first week of September," Matheson said. A lot of it is footwork, creating containment lines by hand. Of the 187,500 acres already blackened by the Rim Fire, more than 43,000 acres had burned inside Yosemite, up 3,000 from Tuesday, according to fire officials. Containment lines have been established around 23 percent of the fire's perimeter. The flames last week forced the closure of a stretch of Highway 120 that leads to the west side of the 750,000-acre (300,000-hectare) park and is the main entrance from the San Francisco Bay area. Tioga Road, the second of the four access routes into the park, was closed to allow fire crews to build containment lines along the road before the blaze approaches, said Yosemite spokesman Tom Medema. "That will limit the access for visitors to and from the east side of the park, quite possibly over Labor Day weekend, which will have a significant economic impact on the area and (be) an inconvenience for visitors," he said. The blaze, the biggest California wildfire since October 2007, is being fought by a force of some 4,100 personnel, backed by teams of bulldozers and water-dropping helicopters. Firefighters plan to burn containment lines from the Hetch Hetchy Reservoir in the remote northwestern section of the park south to Tioga Road to stop the fire from moving further east into the park, Medema said. By Wednesday afternoon, any remaining campers from the Yosemite Creek Campground and Tamarack Flat Campgrounds will be evacuated, he said. The park also closed the Crane Flat Campground. The blaze has been among the fastest-moving of dozens of large wildfires raging across the drought-parched U.S. West that have strained national firefighting resources. Cooler temperatures, higher humidity and calmer winds had been expected to help the firefighting effort Tuesday night, said Alison Hesterly, spokeswoman for the California Department of Forestry and Fire Protection. Later on Wednesday, temperatures were expected to be hot and dry, hitting a maximum of 94 Fahrenheit (34 Celsius) in the area with a minimum of 15 percent humidity, she said. After advancing on the Hetch Hetchy Reservoir for several days, flames got close to the artificial lake on Tuesday. The San Francisco Public Utilities Commission said there was little risk to the reservoir because of the rocky terrain and lack of brush surrounding it. Officials said ash had drifted onto the surface of the reservoir, but testing of samples showed water quality remained healthy. If the water should become fouled by too much ash and soot and require filtration, it can be diverted through a treatment plant near San Francisco before being delivered to customers, officials from the commission said. Most of the homes in the path of the fire have been ordered evacuated or were under advisories urging residents to leave voluntarily or be ready to flee at a moment's notice. The fire has already destroyed dozens of homes and cabins, but no serious injuries have been reported. Writing by Alex Dobuzinskis and Dan Whitcomb; Editing by Cynthia Johnson and Prudence Crowther