Update, 5 p.m.
Crews found a fast-moving grass fire burning along the roadway and were able to stop the forward progress fairly quickly, said County Fire Capt. Dave Zaniboni. The vegetation fire burned 11.5 acres.
Investigators are looking into the cause of the fire, which Zaniboni noted started along a roadway.
Update, 2:20 p.m.
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The fire has grown to 11.5 acres, according to a tweet from Mike Eliason, public information officer for Santa Barbara County Fire.
A vegetation fire was reported near Santa Ynez on Thursday afternoon along Highway 154 and Armour Ranch Road, near the roundabout with Highway 246.
Crews requested air support, including helicopters and tankers, according to emergency radio traffic.
The fire was initially reported as 5 acres and was burning in light fuel — grass and brush — at a moderate rate of spread.
The California Highway Patrol closed eastbound traffic on Armour Ranch Road at the roundabout.
No further details were available. Check back for updates.