California Highway Patrol said Altamont Pass Road was closed between Carroll and Grant Line Road. Drivers should expect delays.
Cal Fire crews in the East Bay battled the fire that erupted to 80 acres before forward progress was stopped.
Firefighters from Cal Fire's Santa Clara Unit (SCU) responded to the fire just after noon, which was burning about 7.5 miles northeast of the city of Livermore.
The fire had scorched less than 5 acres when firefighters first responded. It grew to about 80 acres by 1:30 p.m., when firefighters were able to stop forward progress, according to Cal Fire.
The attack was bolstered by a Cal Fire helicopter and ground crews from the Livermore-Pleasanton Fire Department.
The fire, which was referred to by Cal Fire as the Pass Fire, was about 30% contained as of about 2 p.m.
Altamont Pass Road is a mountainous east-west route that runs just north of Interstate Highway 580.
Firefighters will be on scene strengthening containment lines and putting out hot spots throughout the day, according to Cal Fire.
A Red Flag Warning issued by the National Weather Service was active Saturday through Monday amid forecast of low humidity and high winds between 20-30 mph.
PG&E also advised of potential Public Safety Power Shutoffs because of the increased risk of wildfires.
There were pockets of dozens of PG&E customers in the area of the Pass Fire without power due to preemptive shutoffs, including north of the fire across the Contra Costa County line and farther east, south of Tracy.
Some customers were also without power in Solano County and in eastern Napa County because of Public Safety Power Shutoffs.
Power will remain shut off for those customers until local weather conditions change.
ABC7 Eyewitness News contributed to this report.