SAN FRANCISCO (Reuters) – One of largest fires inrecent California history continued to roar insideYosemite National Park and threatened facilities that supply waterand power to the city ofSan Francisco.

As of Monday morning, hand crews backed by bulldozers andhelicopters dropped water and flame retardant, containing around 15percent of the blaze's perimeter, more than double Sunday's figure.It is one of the 20 largest wildfiresin California history, according to Cal Fire.

Fire managers reported making headway in their 9-day-old battleto curtail flames roaring through dry brush and forests along thenorthwestern edge of Yosemite National Park, putting utilities thatserve the city of San Francisco in danger.

The so-called Rim Fire has charred nearly 150,000 acres or 234square miles – the size of the city of Chicago - since iterupted on Aug. 17, most of that in the Stanislaus National Forestwest of Yosemite. It has forced the closure of the main parkentrance road used by visitors from theSan Francisco Bayarea.

The National Park Service website is posting alertsfor the Rim Fire.

By Sunday afternoon, some 15,000 acres within Yosemite hadburned, prompting the evacuation of 74 campsites in the White Wolfarea of the park, officials said.

The blaze also crept to within 2 miles of a key reservoir, theHetch Hetchy, which is the source of 85 percent of SanFrancisco's water supply, and authorities said they were concernedabout ash contamination from the fire.

Hydropower facilities in the area that provide electricityto San Francisco, about 200 miles to the west, also have beenthreatened.

Two of three power stations that account for all of the city'smunicipal electricity – for public hospitals, transit, CityHall and airport – have been shut down since last Monday. Butthe city has so far made up for the loss by purchasing supplementalpower from the open market and using some of its reserves.

Governor Jerry Brown declared a state of emergency forSan Francisco on Friday due to threats to the city's water supply.He planned to visit the fire zone on Monday to meet with firemanagers and firefighters.

The blaze has destroyed about a dozen homes and 1,000outbuildings, and some 4,500 additional dwellings remainedthreatened. Residents in the tiny town of Tuolumne on thewestern edge of the park were evacuated, but evacuation orders havebeen lifted for the communities of Pine Mountain Lake and BuckMeadows.

The majority of the 1,200-square-mile Yosemite National Park,including the Yosemite Valley area famous for its towering rockformations, waterfalls, meadows and pine forests, remained open tothe public.

The cause of the wildfire remained under investigation. Morethan 2,800 firefighters have been assigned to the blaze, which wasburning over steep terrain through scrub, oak and pine, stoked bystiff winds, high temperatures and low humidity.

The blaze in the western Sierra Nevada Mountains was among thefastest-moving of some 50 large wildfires raging across thedrought-parched U.S. West. The blazes have strained resources andprompted fire managers to open talkswith Pentagon commanders and Canadian officials aboutpossible reinforcements.

(Reporting by Laila Kearney; Writing by Steve Gorman;Editing by Cynthia Johnston and Berenard Orr)