Update, 6:50 p.m.
The Rock Fire off Chimney Rock Road near Lake Nacimiento is 65 percent contained, as of about 6 p.m. Sunday. The acreage decreased to 30 acres, because of more accurate mapping, Cal Fire said in a tweet.
The Mustang Fire in Paso Robles reached 100 percent containment on Sunday afternoon, according to Cal Fire.
The blaze, which burned 37 acres, was one of two that broke out in the North County on Saturday. The other, the Rock Fire, was reported just before 3 p.m. at 14140 Chimney Rock Road, just south of Lake Nacimiento.
Within 30 minutes, the Rock Fire grew to 15 acres. Less than an hour later, the Mustang Fire broke out at 3250 Mustang Springs Road in Paso Robles.
The Rock Fire burned 39 acres and was 40 percent contained as of Sunday morning, according to Cal Fire.