MARIPOSA, Calif. (Reuters) – A wildfire that has forced thousands of Californians to flee their homes exploded in size on Wednesday, threatening a picturesque gold rush town outside Yosemite National Park as dozens of fires scorched the U.S. West.

More than 2,000 firefighters have contained just 7 percent of the Detwiler Fire, which is approaching the town of Mariposa and tiny communities in the foothills of the Sierra Nevada mountains, the Cal Fire state agency said on its website.

The blaze has mushroomed to 46,000 acres (18,000 hectares), an increase of about 20,000 acres (8,094 hectares) compared to the day before, and is threatening some 1,500 structures.

Firefighters are facing “extreme and aggressive fire behavior” with solid walls of flame and sparks from the main blaze setting spot fires in grasslands, the California Department of Forestry and Fire Protection (Cal Fire) said.

Flames have destroyed eight structures southwest of Yosemite National Park and the fire is threatening power lines to the park, but no one has been injured so far, Cal Fire said.

Mariposa’s 2,000 residents were told to leave town on Tuesday after its power and water links were damaged. Hundreds more residents from nearby communities were also ordered to evacuate, officials said.

Many summer vacationers visit Mariposa, which is largely dependent on tourism.

The town, taking its name from the Spanish word for butterfly, was founded during the California gold rush in the 19th century and is surrounded by pine-covered hillsides. It boasts the state’s oldest law court, built in 1854 in a Greek Revival style and topped with a clock tower.

Dan Ostler, a Mariposa business owner, said he was staying behind to offer fire crews bathrooms and water. “It’s something I want to do, I can do. I’ve got my escape route planned,” he told Sacramento’s KOVR television.

Smoke pouring from the Detwiler Fire has drifted as far northeast as Idaho, according to satellite photos from the National Oceanographic and Atmospheric Administration.

The California blaze was among 37 active large fires spread across 12 western states as of Wednesday, according to the National Interagency Fire Center’s website.

Around 4.4 million acres (1.8 million hectares) have been burned since the start of 2017, compared to 2.7 million acres (1.1 million hectares) in the same period last year, according to the website.

Governor Jerry Brown declared a state of emergency for Mariposa County on Tuesday, dispatching resources to the area.