Police are still searching for an Oregon woman who disappeared Sunday while on a hike with her boyfriend.
Allyson Watterson, 20, was reported missing the day after her boyfriend, 21-year-old Benjamin Garland, said the two had become separated while hiking near North Plains.
“We don’t really know how they got separated,” Washington County Sheriff’s Office spokesperson Brian van Kleef tells PEOPLE. “We don’t know exactly what they were doing out there.”
Van Kleef says authorities have not seen evidence of foul play.
“We don’t have any tangible evidence of that at this point,” he says. “Everything is a possibility. Everything is on the table. Nothing is specifically ruled out. We are looking at all the possibilities.”
Van Kleef says search and rescue crews have been looking for Watterson since the morning of Christmas Eve but are now conducting a “more focused and technical search” for her.
The area where the couple went hiking includes open fields, dense thick wooded areas and rural properties with sheds and abandoned vehicles.
“I can see how someone not familiar with the area could easily get lost,” says van Kleef. “She is from a nearby city but I’m not sure if she is familiar with the area.”
Police say a neighbor found Garland asleep in his truck Monday.
“The neighbor whose truck he was found sleeping in gave him a ride back to where he lived,” van Kleef says.
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Garland and his father then went out looking for Watterson and when they couldn’t find her reported her missing, van Keef says.
Garland was later arrested on unrelated charges of theft, fraudulent use of credit and possession of a stolen vehicle, KOIN reports.
He has a hearing scheduled for Jan. 3. It was not immediately clear if he has entered a plea or retained an attorney to comment on those allegations.
Van Kleef says searchers remain hopeful that Watterson will be found alive.
“We are trying to stay positive and stay focused on finding her,” he says. “The longer it goes on I feel like the chances of finding her dwindle, but hopefully we can find her.”
At the time of her disappearance, Watterson, who is about 5 feet 7 inches, was wearing a hooded sweatshirt, black jeans and brown Calvin Klein boots. She was also carrying a red backpack.
Authorities ask anyone who might have information about Watterson’s whereabouts to call the Washington County Sheriff’s Office’s non-emergency number: 503-629-0111.