The wildfire burned nearly 6 square miles Monday afternoon, more than double the 1,500 acres reported in the morning.
The flames were threatening 100 homes in the sparsely populated area, which is dotted with animal pens and shooting ranges. Evacuations have spread into Clayton, including Trail Ride Road, Russelmann Park Road, East Trail Road and Upper and Lower Trail Roads. Oak Hill Lane, Curry Canyon Road and Curry Point Area were all evacuated Sunday. There are 100 homes in Clayton threatened.
The Red Cross set up a center for evacuees at the Clayton Library. Those with horses can go to the Heather Farm Park in Walnut Creek or the Contra Costa Horseman's Association in Concord. Animal evacuation centers have been set up at the Contra Costa County Fairgrounds and the Equestrian Center of Walnut Creek.
As of 11 p.m. Monday the Morgan Fire was threatening to jump the fire containment lines near Morgan Territory and Marsh Creek roads. Around 9 p.m. Cal Fire says everything was under control on the east side of the mountain and then the winds picked up and flames came racing down the mountain toward Morgan Territory Road. Now the road is the last fire break standing in the way of the flames that are several yards away from several homes and horse stables.
Monday night a line of horse owners with trailers were waiting for Cal Fire to let them in to rescue their animals, but the fire is right up to the road so Cal Fire couldn't let them in until it is safe.
"We're trying to evacuate horses out and get some livestock out and see what we can do," said horse owner Emily Sisson. She said she knew of about 40 horses that needed to be evacuated.
Firefighters say Mount Diablo conditions are uncommon because at night the warm air from the heated ground mixes with the cool air from the fog and causes an eddy effect. Monday night that effect caused the winds to kick up and came down the hill, surprising everyone.
There is a mandatory evacuation order on Morgan Territory Road, but not everyone is leaving. They don't have to although it is a mandatory evacuation. Cal Fire said they will be out protecting that road all night long.
Earlier on Monday, the fire was threatening electrical transmission lines, communications infrastructure, and a historic lookout and visitor center at the top of the 3,848-foot Mount Diablo. The Summit Museum was constructed in the 1930s of sandstone from the park.
The fire has spewed a plume of smoke visible for miles. Some East Bay residents have reported ash falling from the sky and several schools cancelled outdoor activities because of the smoke advisory.
"I feel pretty confident that we will be able to get control of this, but not today. It's probably going to be a good couple of days before we can get our arms wrapped around this," said Cal Fire Division Chief David Shew.
The blaze broke out Sunday amid nearly triple-digit temperatures in the early afternoon. The cause is under investigation.
ABC7 News reporters Laura Anthony, Alan Wang, Wayne Freedman, Amy Hollyfield and Matt Keller contributed to this report.
The Associated Press contributed to this report.