The fire broke out at the Peck Road Water Conservation Park around 3:35 p.m., and spread outside the park to a Pick-A-Part salvage yard.
It burned between eight to 10 acres and was contained about 50 minutes later by firefighters from Monrovia, Los Angeles County and Arcadia.
"Our crews were able to make really quick work of it and protect these exposures and stop the fire from spreading," Los Angeles County Fire Department Inspector Scott Miller said.
Smoke and ash spread to nearby cities. No evacuations were issued. No injuries were reported.
Peck Road was temporarily closed between Live Oak Avenue and Lower Azusa Road. The cause of the fire remains under investigation.