Firefighters responded early Friday to a fire reported along Del Dios Highway in Rancho Santa Fe.
The fire, described as a mulch fire by crews, was first reported near power lines around 5:40 a.m.
After they arrived, firefighters canceled an earlier request for air support.
A very large mulch pile started the fire according to firefighters. The heat in the decomposing mulch can spark a fire, crews told NBC 7.
Crews will be in the area for several hours as they spread out the mulch and extinguish the flames.
Ten engines were called to the scene. San Diego Fire-Rescue was on standby with its two fire helicopters.
No homes were threatened by the fire.
Crews from San Diego Gas and Electric said there was no affect on the nearby power lines not affected by fire but smoke can sometimes be an issue.