The fire started at about 9:50 p.m. in a cluster of pine trees on Faria Hill between Faria Avenue and Higuera Avenue, Battalion Chief Jim Parrott said.
An explosion was heard in the area around the time the fire started that fire officials believe was likely illegal fireworks, Parrott said.
The blaze quickly climbed the steep, grassy hill and was headed for about 20 homes, so firefighters called for a second-alarm response, Parrott said.
"We're lucky there was no wind," Parrott said. He noted that the steepness of the hill made the fire move faster and made it more difficult for firefighters to put out.
Crews walked up the hill carrying hose lines while other units stood by the homes at the top of the hill and protected them.
Two inmate hand crews from Cal Fire and the Marin County Fire Department cut a permanent line around the perimeter to contain the blaze, Parrott said.
A total of 50 firefighters from the Pinole Fire Department, the Rodeo-Hercules Fire District, the Contra Costa County Fire Protection District, the Crockett-Carquinez Fire Department, Cal Fire, the Marin County Fire Department and the El Cerrito Fire Department had the fire under control in about an hour.
No injuries were reported and no structures were damaged. The fire was still under investigation today.