President Obama called California Gov. Jerry Brown on Sunday to receive an update on the wildfires in California, including the Rim Fire on the edge of Yosemite National Park, which has scorched more than 200 square miles and threatens the power grid that supplies San Francisco.

“The president expressed his gratitude for the brave men and women working tirelessly to combat this devastating fire,” the White House said in a readout of the phone call.

Obama also reiterated his commitment to providing federal resources to support the ongoing state and local response. There are 3,400 firefighters trying to protect mountain communities in the path of the giant blaze and thousands more deployed to combat other fires across the West.

On Friday, a Federal Emergency Management Agency team specializing in fighting wildfires arrived in California, and FEMA approved a cost-sharing assistance grant.

The still-raging fire was 15 percent contained by Monday morning – up from 7 percent the previous night, officials said.

Fierce winds gusting up to 50 mph are making the fight difficult as flames jump from treetop to treetop across steep, rugged river canyons, making the blaze one of the biggest in California history. Many air districts are issuing health warnings as the smoke covers areas across Northern California.

The popular hiking and tourist destination of Yosemite Valley, the part of the park known for its dramatic rock formations and waterfalls, remained open Monday as firefighters continued to try to contain the Rim Fire about 20 miles away. The fires also threatened the park’s towering sequoias, prompting park employees to take extra precautions to protect the groves.

Over the weekend, officials realized that the fire was threatening the power grid that supplies San Francisco, prompting Brown to declare an emergency for the city. So far the city has been able to keep the power on, even though Brown said Bay Area utility officials were forced to shut down transmission lines and warned of further potential disruptions.