Fire crews used aircraft to extinguish a three-acre brush fire along Highway 101 south of Los Osos Valley Road on Friday afternoon.
No injuries or property damage was reported, but smoke caused traffic to back up on the highway through much of San Luis Obispo.
According to a Cal Fire spokesman, a report of the fire came in at approximately 2:06 p.m. from the Johnson Ranch area south of Los Osos Valley Road near the Higuera Street exit. Crews from Cal Fire and the San Luis Obispo Fire Department responded, and a Cal Fire plane and a Los Padres National Forest helicopter dumped orange and black retardant on the area.
Officer Laura Browning of the California Highway Patrol said traffic stalled in the north and southbound lanes beginning at California Street through the Higuera Street exit to poor visibility from the smoke.
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Cal Fire crews were cleaning up the scene until early Friday evening.
The cause of the fire remains under investigation.