VERLOT — He urges hikers to bring everything in their packs, even car registration papers.

A fresh spate of vehicle break-ins have been reported at trailheads along the Mountain Loop Highway this summer.

Albert Frederick, 46, has hiked and climbed peaks reached off the highway for 10 years. He said car prowls have always been a concern, but this summer especially.

People have been warning others on the Washington Hikers and Climbers Facebook page that is followed by more than 68,000 outdoor enthusiasts.

One man said he has seen about 25 cars broken into over the past few weekends near Goat Lake, Barlow Pass and Mount Pugh. Several windows were smashed. A couple of tires were slashed. Some drivers found holes in the gas tanks, he reported.

“It’s not just one or two cars,” Frederick, of Mountlake Terrace, said. “It’s a growing concern.”

A woman from Alaska told Frederick she had recently hiked at Goat Lake. While she was on the trail, her car and two others were broken into. Cell service is spotty along the highway, but she was able to flag down a Snohomish County Sheriff’s deputy.

Earlier this month, the sheriff’s office went to social media to warn that there have been more car prowls at trailheads, parks and beaches lately. The U.S. Forest Service has noticed the same pattern, specifically along the Mountain Loop Highway.

One woman has resorted to taping a note on her windshield at trailheads. It reads: “Smile. Trail cam in the trees watching over cars.”

“It’s kind of a damper to people who want to go out there. It’s a beautiful area,” Frederick said.

He hikes trails along the Mountain Loop Highway to train for longer treks. In the past three years, he has climbed all five volcanoes in Washington state.

“Mountain Loop is one of those hidden gems. Not too many people go up there,” Frederick said. “But with the vandalism, it’s a gamble. Do you take the chance or not?”

He has seen sheriff’s deputies and forest rangers patrolling the area, but the trailheads are often secluded. Sometimes cars have to travel a couple of miles off the highway along an unpaved road.

Frederick wasn’t sure of a solution.

People in the Facebook group proposed a few ideas.

They suggested parking lot attendants and decoy vehicles. Some offered to donate cameras to law enforcement to help them catch the prowlers.

The Forest Service provided tips for those heading to the mountains. Lock valuables in the trunk of the car, or leave them at home. Don’t hide car keys on or near the vehicle. Take note of any suspicious vehicles, including the car’s description and license plate number. Unusual activity also can be reported to a local law enforcement agency or the Forest Service.

Always report car break-ins to the police. It helps them pinpoint crime patterns.

Forest Service spokeswoman Tracy O’Toole offers one more piece of advice: Don’t leave a hiking itinerary on your dash. Leave it with friends, family or at a ranger station.

Reporter Eric Stevick contributed to this story.

Caitlin Tompkins: 425-339-3192; ctompkins@heraldnet.com.