81-year-old John Chesley wandered away from his home last Saturday, and never came back.
Officials said he recently started showing signs of dementia.
Rescuers spent most of the day indoors Thursday trying to come up with a new game plan to find Chesley.
The Butte County Search and Rescue team said they spent the day going over all of the information they received this week trying to find Chesley.
They said no clues have been discovered.
Rescuers said Chesley was in the Navy for more than 30 years, and that could help his survival.
They also said the rain could complicate things.
"The rain hampers our search efforts,” said Lieutenant Kevin Lucero of the Butte County Search and Rescue team. “It washes away potential clues and evidence we want to locate and start collecting as soon as possible. This will point us in a positive direction of where he is."
Lucero said he doesn't know when rescuers will be out again to look for Chesley.
Chesley is described as a white man standing five foot eight inches, weighing 140 pounds with brown eyes and short gray hair.
He was last seen a blue flannel shirt, jeans and white shoes.
Anyone with information on his whereabouts is asked to call the Butte County Sheriff's Office at 530-538-7321.