A grass fire that burned two acres at Pearson Arastradero Preserve on Thursday (July 28) afternoon is being investigated by the Santa Clara County Arson Task Force, Palo Alto Fired Battalion Chief Chris Woodard confirmed on Friday.

The blaze was spotted by a passerby at about 2:40 p.m. in an area near Interstate Highway 280 and Arastradero Road and took about 30 minutes to extinguish.

The arson task force is "looking at the fire to make sure it was not arson," Woodard said, as no cause has been determined.

Woodard said residents should clear brushy areas by 3,200 feet and around their residences by at least 100 feet, which is recommended to keep a fire from reaching a home.

"Be aware of anybody out there. This is the time of year when people who set fires are active," he said.