Firefighters set backfires near the south entrance of Yosemite National Park to deprive the Washburn Fire of fuel/NPS

Aerial bombardments, bulldozers, hand tools, and even artificial clouds of humidity are being used at Yosemite National Park to combat the Washburn Fire, which continues to grow in size, fed by acres and acres of dead and downed trees and thick ground layers of combustible forest litter.

In the Mariposa Grove of Giant Sequoias, perhaps the most iconic sequoia grove in the world with more than 500 mature sequoias, snaking yellow hoses are feeding water into sprinklers to both wet the forest floor and boost the ambient humidity, while firefighters have been using chainsaws to slice up and move downed trees away from standing sequoias, and also were raking flammable forest duff away from the giants.

But the fire, which was spotted Thursday, had grown to cover roughly 3,200 acres as of Tuesday morning and just 22 percent of the fire's perimeter had been contained. Much of the blaze was in the Yosemite Wilderness, a rugged landscape that makes it hard for firefighters to work on the ground, according to the daily fire briefing. In that area, air tankers have been dropping tens of thousands of gallons of retardent on the flames. So far, six air tankers have been involved, including two DC-10s that have been taking off and reloading from the McClellan Air Base in Sacramento, California. These planes are capable of dropping upwards of 4,000 gallons of retardent or water on the fires.

Closer to the Wawona area, which was evacuated, bulldozers have been gouging fire lines in a bid to stop the flames from reaching the structures there. The weather was not helping the nearly 550 firefighters tackling the fire. A drying trend was moving into the region, daily high temperatures were expected to approach 90 degrees Fahrenheit, and relative humidity had dipped to 20-25 percent. Over the next two days, the expectation was for "[W]arm and dry conditions, combined with poor-fair night time relative humidity [to] produce conditions for active to very active fire behavior on uncontained portions of the fire perimeter. Expect sustained backing, active flanking, more frequent torching with spotting, and short headfire runs likely."

"Spotting" -- the carrying of embers on the winds -- could reach a half-mile ahead of the active fire, the briefing said.

The cause for the fire was being investigated. 

The bulk of Yosemite National Park, outside of the southern tip at and below Wawona, remained open, and access to Yosemite West was accessible from the north. Visitors to those areas were told to expect smoky conditions.

The area from Wawona down to the south entrance of Yosemite has been evacuated due to the Washburn Fire/NPS