Fire crews from Ventura and Los Angeles counties are battling a rapidly growing vegetation fire in Holser Canyon, near Lake Piru, in 100-degree heat. The blaze, called the Canyon Fire, is estimated to be at 1,

The Canyon fire broke out around 2 p.m. near Holser Canyon Road, northeast of Piru. By Thursday night, it was pushing east toward Castaic and Interstate 5.

Andrew Dowd, the spokesman with the Ventura County Fire Department, said an estimated 150 to 200 firefighters were on the scene. “We’re doing a significant initial attack,” Mr. Dowd said.