A fire scorched 12 acres of grass off Highway 49, a quarter-mile north of the overlook at New Melones Reservoir in Calaveras County Wednesday afternoon.
It is believed to have been started at the roadside at about 12:27 p.m. by a hot catalytic converter on a vehicle. It was contained at 3:54 p.m.
"They did a great job of stopping the fire," said Kary Hubbard, information officer and Tuolumne County fire marshal. "It was on a steep upslope in the warmer part of the day, and that's a bad time for a fire to start."
Hubbard said sparks from vehicles are common causes of roadside fires and advised people not to pull off the highway into grassy areas.
The fire also serves as a reminder of how easily dry grass burns. Hubbard urged people to be careful with outdoor power equipment such as mowers, chain saws and weed trimmers, and to use them in the early morning hours when the humidity is highest and the temperatures are cool.
California Highway Patrol Officer Tom Wills said the highway remained open during the fire, and no major traffic problems were reported.
Responding were eight engines and a bulldozer from California Department of Forestry and Fire Protection, two inmate hand crews from Vallecito Conservation Camp, a helicopter from Columbia Air Attack Base, engines from Altaville-Melones Fire Protection District and a prevention officer from CDF.
The catalytic converter is an anti-pollution device that can reach extreme temperatures during operation.
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