The Rim Fire, which has devoured nearly 161,000 acres, is also threatening San Francisco's key water and power sources.
The Yosemite wildfire rages on in California as the wildfire doubles in size and Fire crews fight to save Yosemite as more Firefighters are sent in to battle Yosemite wildfire.
The wildfire, which was 20% contained Monday night, was spreading primarily to the east and threatened to grow amid extremely dry conditions and hot weather.
As many as 20 helicopters and air tankers were aiding the efforts of 3,600 firefighters.
The fire continued to spread Monday toward a key part of San Francisco's water supply: the Hetch Hetchy Reservoir, which lies within Yosemite and is just east of the flames.
Yosemite, with hundreds of campground sites and lodging units, had nearly 4 million visitors last year, and the park typically has 15,000 visitors on a busy summer weekend.
While the Rim Fire has consumed at least 12,000 acres in the northwest section of the park, so far it has had little or no direct impact on Yosemite Valley, a popular spot for tourists and home to many of the famous cliffs and waterfalls in the park.
Wildfires are sometimes called "wildland fires."
Wildfires can originate from a dropped match, cigarette embers, campfires, exhaust sparks from a train, or arson.
Many wildland fires are ignited by lightning.
There are no official rules, but the first responders usually name a fire after a meadow, creek, city, or type of plant they see.
Wind, temperature, and humidity all influence wildfires. Strong winds push flames toward new fuel sources. Wind can pick up and transfer burning embers and sparks, starting "spot fires."
During the day, sunlight heats the ground and warm air rises, allowing hot air currents to travel up sloped landscapes. At night, the ground cools and air currents travel down the slopes.
Humidity dampens fuel, slowing the spread of flames. Humidity is greater at night, so fires usually burn less intensely then.
Large fires can create their own winds and weather, increasing their flow of oxygen.
Its everyone's responsibility to be careful with fire so we don't loose a national treasure like Yosemite National Park.