The Contra Costa County Fire Protection District on Saturday morning reported responding to at least 13 fires since Friday night.
At least three of the fires were structure fires, two were vehicle fires, and there were several vegetation fires reported, according to ConFire.
Of the fires reported, at least three were known to have been caused by illegal fireworks, according to ConFire officials.
ConFire is urging residents to have a safe and fireworks-free Fourth of July.
Firefighting crews were called to put out fires in Pittsburg, Bay Point, San Pablo and Rodeo, officials said.
Crews that extinguished the Pittsburg fire determined fireworks were the cause.
The Contra Costa Fire District said fireworks also started a grassfire after 10 p.m. Friday, between Levee Road and the railroad tracks in Bay Point.
Trains were slowed through the area for safety.
The Rodeo-Hercules Fire District was assisted by the Pinole Fire Department, the Contra Costa County Fire Department, and the Crockett-Carquinez Fire Department at a blaze reported about 10 p.m. that burned down a barn at the historic Claeys Ranch in unincorporated Rodeo.
A vegetation fire was also reported at 18th Street and Dover Avenue near Dover Elementary School in San Pablo at about 9:30 p.m. Friday.
Investigators have not yet officially announced how many of these fires were connected.