ELDORADO CANYON STATE PARK, Colo. -- Friends and family of a Marine who disappeared last week after injuring his head while hiking plan to keep looking for him and gathered Tuesday to coordinate their efforts.

Boulder County authorities have called off the ground search for 21-year-old Lance Hering -- who disappeared last week in Eldorado Canyon State Park. A hiking companion said he went for help the next morning after Hering fell and hurt his head while the two were bouldering on Aug. 29. Hering was gone when rescuers returned three hours later.

Hering's family thinks he might be disoriented from the fall. He experienced a memory lapse after a head injury when he was 11.

Authorities think Hering might have reverted to a military mindset and gone for cover. Hering returned from Iraq a month ago and is due back at Camp Pendleton in California in a couple weeks.

Several tips came in to the Boulder County Sheriff's office from people who said they may have seen Hering. Deputies said they checked out every one of the tips, but none of them led to Hering.

"It is perceived that this man is moving. There's water up there," said search leader Rick Baum. "He has access to that water and it would appear to us (that he can) stay alive."

Deputies said they know he walked out, but the question now is whether it was accidental or intentional.

"With his head injury he could have amnesia or perhaps reminiscing back to combat situation so he's using survival, resistant and escape tools," said Baum.

Professional search crews spent four days combing the canyon and said they didn't believe he was in the area and may have wandered off. They also searched the swift-moving South Boulder Creek, which runs through the park.

Friends gathered near the park on Tuesday to coordinate their search efforts.

Fliers will also be put up at businesses in the area in hopes that Hering may see them and realize his predicament.

The Boulder County Sheriff's Department said a nationwide missing person bulletin will be put out.