UPDATE (8:12 P.M.) - The fire is reported to be 50 percent contained with two engines remaining on scene.
The fire's size is now estimated at 45 acres after crews were able to walk the entire area.
UPDATE (5:35 p.m.) - The fire is now reported to be 40 percent contained, according to CAL FIRE.
UPDATE (3:30 p.m.) - CAL FIRE reports forward progress of a fire that burned 54 acres Friday south of Atascadero has been stopped and the fire is 30 percent contained.
Fire investigators determined that a pickup truck driving northbound on Highway 101 just before 12:30 p.m. suffered a broken drive line, and the broken parts sparked a fire in the center divider of the highway. The fire then spread to both sides of the 101.
No structures were damaged. CAL FIRE says firefighters were able to protect 20 homes that were initially threatened by the flames.
Evacuation orders for people living on Santa Margarita Rd. and Powerline Rd. have been lifted.
Highway 101 was heavily impacted throughout the afternoon, but as of 3:30 p.m., all northbound lanes of the highway were open and just one southbound lane at Santa Barbara Rd. remained closed.
UPDATE (2:52 p.m.) - CAL FIRE says forward progress of the fire that broke out Friday south of Atascadero has been slowed. Air operations have been halted and firefighters are mostly in mop-up mode.
While CHP and Caltrans are slowly starting to reopen the lanes of Highway 101 to motorists, traffic remains backed up through the area.
Fire officials say they are investigating a pickup truck crash as the possible cause of the fire.
UPDATE (2:30 p.m.) - The San Luis Obispo County Sheriff's Office says residents who were evacuated as a result of the fire will be allowed to return to their homes at 3:15 p.m. All roads that were closed will also be reopened at that time.
CHP says all southbound lanes of Highway 101 should be open to traffic soon, once the pickup truck that spun out when the fire started is removed.
The northbound side of the highway will remain impacted for an unknown time.
UPDATE (1:55 p.m.) - CAL FIRE says 54 acres have burned in a fire that broke out off Highway 101 south of Atascadero on Friday.
The fire started just before 12:30 p.m., approximately two-and-a-half miles south of Santa Barbara Rd.
CAL FIRE says there are about 50 homes in the area and 20 were immediately threatened, but firefighters say crews have been able to protect those homes from the flames.
CAL FIRE PIO Adan Orozco says containment lines appear to be holding, but there is no estimated containment at this time.
People driving through the area should expect delays. Caltrans advises drivers to use El Camino Real/Highway 58 as a detour.
Firefighters expect to remain on scene throughout the night.
UPDATE (1:40 p.m.) - CAL FIRE says the fire that broke out Friday afternoon along Highway 101 south of Atascadero has burned 40 acres.
UPDATE (1:27 p.m.) - Caltrans says one lane of Highway 101 in each direction has been closed as a result of the fire. El Camino Real/Highway 58 is advised as a detour.
The sheriff's office says it also sent a Reverse 911 announcement to residents from Santa Barbara Rd. south to Garden Farms and east, alerting them to the fire.
— CAL FIRE SLO (@CALFIRE_SLO) August 16, 2019
UPDATE (1:05 p.m.) - The San Luis Obispo County Sheriff's Office is evacuating portions of Santa Margarita Rd. and Powerline Rd. as a result of a fire that broke out along Highway 101 south of Atascadero.
The fire, which broke out just before 12:30 p.m. Friday after a pickup truck crashed, was burning on both sides of the 101, approximately two-and-a-half miles south of Santa Barbara Rd.
UPDATE (12:53 p.m.) - CAL FIRE says the fire is currently estimated at 5 acres and structures are threatened.
Caltrans has issued a SIG Alert for that section of Highway 101. Drivers should expect delays and traffic control.
(12:33 p.m.) - Emergency crews were responding to reports of a pickup truck crash that sparked a brush fire along Highway 101 north of Highway 58.
The crash was reported just before 12:30 p.m. Friday on the northbound side of the freeway between Santa Margarita and Atascadero.
The California Highway Patrol reported that multiple reports stated that the fire was burning on both the northbound and southbound sides of the 101.
This is a developing story and will be updated with new information as it becomes available.