Investigators have determined a 13-acre grass fire on Monday in Menlo Park near Facebook is suspicious, fire officials said Friday.
Firefighters arrived at 3:37 p.m. at the Kavanaugh Tract, which is adjacent to Adams Drive and the Menlo Business Park.
Fire officials described the fire as unusual at an unusual time of year.
Investigators determined the fire started at a homeless encampment through some form of human action, according to fire officials.
Firefighters requested a second alarm at 4:03 p.m. as 20 to 25 mph winds whipped up the blaze. It quickly spread across a marshy bog and threatened to jump the four-lane University Avenue into an East Palo Alto residential neighborhood at Purdue Avenue, fire officials said.
University Avenue, which runs between the Bayfront Expressway and the Dumbarton Bridge, was closed for several hours as crews brought the fire under control by 6 p.m.
The fire affected evening commuters, according to fire officials.
Firefighters got help from a private photographer who flew his drone over the fire. Pictures from the drone helped fire officials adjust their tactics and deployment of firefighters and equipment to extinguish the fire.
The fire district is pursuing its own drone system through the Federal Aviation Administration.