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A northern California region marked by towering redwood trees and mountains rising out of the Pacific is the focus of an intensive search for a suspect in the shooting deaths of his wife and two young daughters.

Shane Franklin Miller, considered armed and dangerous, grew up in coastal Humboldt County and authorities say that his ability to fortify himself in an area so remote it's called the "lost coast" makes searchers vulnerable.

"It would be easy to hide out up there," said local resident Phil Franklin, one of hundreds ordered to lock doors and shelter in place as the manhunt expands.

Authorities believe the 45-year-old Miller has taken refuge somewhere in the area around Petrolia since his truck was found nearby on Wednesday.

His family was found slain Tuesday night in the rural community of Shingletown, a 200-mile drive through mountains to the east.

A sheriff's investigator said Miller's retreat into the mountainous woods creates a dangerous situation for officers trying to track him.

"It's almost like warfare," said Lt. Dave Kent of the Shasta County Sheriff's Office, which is handling the investigation.

To imagine the ruggedness of the landscape think "Jurrasic Park" because some of the movie was filmed there. Many residents live off the grid on unmarked back roads often shrouded in a coastal fog.

Folks in this community of 200 miles north of San Francisco have been ordered to leave a contact number tacked to their front doors if they evacuate so that so law enforcement can verify their safety.

Schools were closed.

"We assume he's still in the valley, but he could have gotten help from somebody," said Franklin who runs the Petrolia Guest House, one of the few businesses in a town so-named because the first California oil well was drilled there. "We're all locked down here. We're supposed to call 911 if we see anything suspicious."

On Thursday tactical search teams from Shasta, Humboldt and Mendocino counties asked for assistance from other agencies, including the swat team from Pelican Bay State Prison in Crescent City near the Oregon border that is trained in apprehending escaped prisoners, said Terry Thornton, spokeswoman for the state prisons. They were instructed to meet at the incident command post, the Petrolia Volunteer Fire Department, at 6 a.m. Friday, she said.

Authorities say he is familiar with the tree-lined canyons so steep that only one paved, pot-holed road serves the area. They suspected he might be heading to a cabin he frequents, but there were no sightings reported on Thursday.

Like Franklin, most of the residents are armed because law enforcement patrols are rare in this community built on a peninsula that juts into the Pacific.

"The county is strapped for money so we don't have police protection out here. We all contact each other if something occurs so we can coordinate help," Franklin said.

A woman who identified herself as Miller's mother told the Associated Press on Thursday that she had not communicated with her son since the shooting and was unaware of problems in the marriage.

Miller is familiar to law enforcement. He once tried to make a living growing one of the region's biggest cash crops -- marijuana. In 1996 he was convicted of felony cultivation in a county known worldwide for the high quality pot grown in the same hard-to-reach forests authorities now are combing.

In 2002, Miller was charged in San Francisco with making and selling marijuana for distribution, being a felon in possession of a firearm, possessing a machine gun and money laundering, according to court records. He pleaded guilty to being a felon in possession of a gun and was sentenced to three years and 10 months in prison. He was released in May 2007, according to the federal Bureau of Prisons.

He served 46 months in federal prison for being a felon in possession of a firearm, court records show.

He apparently stayed off the radar of law enforcement until 7:45 p.m. Tuesday, when Shasta County Sheriff's deputies received a call from his house. When they arrived, they found the bodies of Miller's wife, Sandy, 34, and two daughters, Shelby, 8, and Shasta, 5.

All three had been shot multiple times, said Lt. Kent.

Kent said investigators had not determined who placed the call, but he said it was from one of the victims as the shooting was in progress.

Authorities also have not recovered the gun, or guns, believed to have been used in the shooting, but Kent said more weapons were found in the house.

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AP Researcher Jennifer Farrar and reporters Tracie Cone and Sudhin Thanawala contributed to this report.