MARIPOSA, Calif. — Smoke had turned the sun a deep glowing red by the time a Dutch tourist, Trees Duipmans, and her three teenage children reached a campground outside Yosemite National Park on Sunday. Yesterday, they decided it was time to go.

“There was ash falling on our tent. We think we will go to the beach,” Ms. Duipmans said.

A wildfire burning almost completely out of control yesterday outside the famed park has charred more than 42 square miles, destroyed 12 homes, and shrouded many an iconic vista with smoky haze. Some visitors toughed it out, while others packed their bags.

The blaze, marching through steep, dry terrain, has forced the evacuation of about 300 homes in the nearby towns of Midpines and Coulterville and is threatening about 2,000 others.

“This is some of the most difficult territory you can find in California for fighting fires,” the chief of the Madera-Mariposa Unit, Mikel Martin, said. “That country is so steep you could almost say it’s straight up and straight down.”

The fire was 10% contained yesterday as it burned about 12 miles west of the park, which remained open. Highway 140, one of three highways leading into Yosemite from the west, was closed for part of the day to allow air tankers to drop fire retardant on the road.

“It’s definitely smoky and you can’t see much,” a park spokeswoman, Kari Cobb, said. “If you have any respiratory problems we are saying avoid strenuous activity.”

A manager at a hostel in Midpines popular with European backpackers, the Yosemite Bug, said most guests had left over the weekend. But a few brave travelers stayed on yesterday to try to spot Yosemite Valley’s celebrated granite peaks through the smoke.

“Some of them just don’t care, they just want to see the beauties of Yosemite,” a manager, Carrie Kidwell, said. “We had guests in here this morning going to the park, and I advised them to take their things with them because we don’t know which way the wind’s going to shift between now and when they get back.”

At the peak of summer, as many as 4,000 visitors a day stream into the park. Officials didn’t expect the fire would keep many away.

“People are out there hiking, the campgrounds are full, everyone is taking the smoke in stride,” a park ranger, Scott Gediman, said.

Power has been out since Saturday in the park and in the outlying community of El Portal on the park’s western boundary. Hotels in the area are open and running on generators.

California has been dogged by wildfire since June, and hot, dry conditions have turned flare-ups into prolonged fire fights. While many earlier blazes were ignited by a massive lightning storm, the fire outside Yosemite was sparked by a target shooter.

High temperatures are expected to remain in the low- to mid-90s, with low humidity and afternoon wind, a National Weather Service meteorologist, Dan Gudgel, said yesterday.

“It’ll be a challenging fire for them to fight,” Mr. Gudgel said.

There are currently 3,000 firefighters on the scene, some from as far away as Greece.

Outside the town of Midpines, Tony Romero ignored mandatory evacuation orders together with his brother John.

“I’m fighting just to save my own stuff,” Mr. Romero said by phone. He stayed up late into the night cutting tractor lines in the dirt around his house, creating a natural fire barrier. “Nothing’s really flared up in my yard or around my house so far, but we could hear the fire crews around all night.”