Crews make progress against Rim Fire raging in Yosemite National Park area in California

Fire now 234 square miles in size

TUOLUMNE CITY, Calif. - Officials say fire crews made progress overnight against a large wildfire threatening San Francisco's water supply, several towns near Yosemite National Park and historic giant sequoias.

Stanislaus National Forest spokesman Jerry Snyder said containment of the Rim Fire was at 15 percent on Monday morning, up from 7 percent the previous night.

The fire did continue to grow, however, and is now 234 square miles in size.

Snyder said crews are being helped by the fire's movement into less forested areas and cooler temperatures caused at least in part by the shadow cast by the large plume of smoke from the blaze.

About 4,500 structures and Hetch Hetchy Reservoir, the source of San Francisco's famously pure drinking water, remain under threat.