Crews stopped forward progress on a 15-acre fire on the side of eastbound Highway 4 in Concord on Thursday afternoon, according to the Contra Costa County Fire Protection District.
The blaze was reported at 1:09 p.m. alongside Highway 4 just east of Willow Pass Road.
The forward progress had been stopped about an hour later, but fire crews remain at the scene, and the blaze reportedly was 75% contained as of Thursday evening.
County fire officials wrote on Twitter that the blaze is the largest of the season to date and "an early indicator of what is to come with Red Flag conditions this weekend."
