BOISE, Idaho — After generating Amber Alerts across the West, the frantic search for a kidnapped teenager and her alleged captor shifted Friday to a remote part of Idaho where the two were believed to be trekking through the wilderness.

The break came after suspect James Lee DiMaggio’s blue Nissan Versa was found in central Idaho about 8 a.m., San Diego County Sheriff Bill Gore said. Federal, state and local authorities were scouring the Frank Church — River of No Return Wilderness in Valley County, where the vehicle was found.

A group of horseback riders told local authorities they spoke to two people believed to be DiMaggio and his alleged captive, Hannah Anderson, 16. The riders came across the pair Wednesday morning but said it wasn’t until they returned later that day that they realized the girl may have been Anderson.

The witnesses said the man and girl had a tent and backpacks but looked out of place in the rugged terrain because they had light camping equipment, Gore said.

The witnesses said the girl appeared to be well, he added.

“I’m very confident and I think we should all be optimistic that she appeared to be in somewhat good health and alive on Wednesday,” Gore said.

They found the car Friday “just off a road,” covered in brush, Gore said. Its license plates had been removed but it was identified using the vehicle identification number, he said.

Authorities planned to use bomb and arson technicians to search the vehicle to render it safe, he said. Earlier this week, sheriff’s officials warned that the vehicle might be rigged with explosives. The vehicle, Gore said, was not destroyed.

The brush “was an attempt to hide it, to keep it out of plain view,” he said.

“We’ve got to assume he is armed, and that is the word we’ve put out to everybody,” Gore said.

Locals said the area is difficult to navigate, especially to people not familiar with the terrain.

Cheryl Bransford, 62, who works as a wilderness guide out of Ya-Hoo Corrals at Payette Lake, north of Cascade, described the terrain as very steep, with areas of “almost jungle-like” thick vegetation.

The River of No Return Wilderness contains more than 2 million acres of federally designated land, marked by rivers, deep canyons and mountains.

Upon receiving the Amber Alert on Friday morning, Bransford said she and other outfitters started locking unused vehicles, which they usually don’t do.

She also took another precaution.

“I keep a .357 within minutes away — loaded,” she said.

The case began Sunday after the body of Hannah’s mother, Christina Anderson, was found in the garage at DiMaggio’s burning San Diego County home. The body of a boy — now confirmed to be that of Hannah’s 8-year-old brother, Ethan — was found in the home.

The case drew national attention as the search for the pair widened. An Amber Alert, originally issued in California, was later broadened to Oregon, Washington and Nevada. Idaho was included Friday morning.