Yosemite Fire 'Poses Every Challenge There Can Be'

An inferno raging on the northern border of Yosemite National Park is slowing its advance toward mountain communities as firefighters scramble to bulldoze fire breaks.

The fire is now nearly 210 square miles and only 7 percent contained.

State and federal fire officials are focusing fire break containment efforts in the communities of Ponderosa Hills, Twain Hart and Tuolumne City.

Local resident Ike Bunney said he has evacuated horses from his dude ranch as bulldozers work near his property.

The fire is edging closer to the Hetch Hetchy Reservoir, where on Sunday ash was falling like snowflakes on the source of San Francisco's famously pure drinking water. City utility officials say that so far the water is safe, but they continue to monitor it.

The fire started Aug. 17. The cause is unknown.