CLAYTON -- As the Mount Diablo fire reached 95 percent containment Thursday and crews shifted their attention to cleaning up and preventing erosion and mudslides, authorities announced that target shooting had been found to be the cause of the blaze.
Cal Fire spokesman Steve Kaufmann would not identify the source of the shooting that ignited the blaze, which burned into its fifth day Thursday, having torched more than 3,000 acres of land. The Marsh Creek Detention Facility has a firing range, but the fire started on the west side of Morgan Territory Road, separated from the range by more than half a mile and a small group of homes.
The area burned had been largely untouched by flames since the 1930s, a parkland official said. The scarred mountain was left looking like a war zone of blackened hillsides dotted with skeletons of trees.
Areas once covered in thick brush now appear more like the surface of the moon, a recipe for erosion and mudslides come rainy season, said Tina Rose, a Cal Fire spokeswoman.
"When there's no vegetation the rains come and it starts a cascading water slide effect," Rose said. "When there's trees and grass it's like a sponge that soaks it up."
Crews will reseed the charred land and, to control the flow of water down hills, use an erosion control technique known as a water bar on the fire line, the rim around the fire firefighters dug with picks and bulldozers to remove all vegetation to contain the blaze. The process could take weeks, Rose said.
As of Thursday, the Morgan Fire, which scorched 3,133 acres, was 95 percent contained. Officials expect it to be fully contained by Friday, but there are still several hot spots to extinguish.
"Until the last shovel full of dirt gets on that piece of land and we know it's dead out, the incident commander won't call it 100 percent," Rose said.
No homes were damaged or lost, and residents who were ordered to evacuate 75 nearby homes returned Tuesday, when the fire began to slow. About 1,300 firefighters have battled the blaze since Sunday; many have left to go back home or fight other fires, including the 8,000-acre Clover Fire in Shasta County. .
Meanwhile, Mt. Diablo State Park is set to reopen Monday, said Dave Matthews, public safety coordinator for the Diablo Valley District of the state park system. Workers are planning to repair and rebuild restrooms, trails, picnic tables and campgrounds damaged by the fire, he said. Mother Nature will take care of the rest.
"Fire is, of course, a part of our natural process," Matthews said. "It's pretty amazing. In a year or two from now you will have a hard time knowing there was a fire."
The cause of the fire remains under investigation, though Contra Costa Fire District Capt. Robert Marshall said investigators have ruled out natural causes such as lightning strikes.
Staff writer Katie Nelson contributed to this story. David DeBolt covers breaking news. Contact him in Richmond at 510-262-2728. Follow him at Twitter.com/daviddebolt.