Calmer weather in Northern California helped firefighters battle a wildfire threatening thousands of mountain homes Monday in the Sierra Nevada.
The Mosquito Fire in the foothills east of Sacramento spread to nearly 73 square miles, or about 46,500 acres, with 10% containment, according to Cal Fire.
Forecasters predicted a respite from the hot and gusty weather that dogged firefighters last week, but possible fuel sources from fine grass to big trees remain very dry and flammable, according to a Cal Fire incident report Sunday night.
After a reconnaissance flight Sunday afternoon, Incident Commander Rick Young said that although the fire's growth had slowed, "where it was burning, it was really burning."
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More than 5,800 structures in Placer and El Dorado counties were under threat and some 11,000 residents of communities including Foresthill and Georgetown were under evacuation orders.
The Mosquito Fire also has covered a large portion of the Northern Sierra region with smoke. State health officials urged people in affected areas to stay indoors when possible. Organizers of the Tour de Tahoe canceled Sunday's annual 72-mile (115-km) bicycle ride around Lake Tahoe because of the heavy smoke from the blaze more than 50 miles (80 km) away. Last year's ride was canceled because of smoke from another big fire south of Tahoe.
The Mosquito Fire's cause remained under investigation. Pacific Gas & Electric said unspecified "electrical activity" around the time the fire was reported on Tuesday.