CASCADE - A car belonging to a man suspected of killing a California woman and her young son and then fleeing with the 16-year-old daughter was found in the Idaho wilderness on Friday after a horseback rider reported seeing the man and girl hiking in the area two days earlier, authorities said.

The rider said he saw two people who matched the description of the pair near Morehead Lake, in an extremely rugged backcountry area 70 miles northeast of Boise sometime around noon Wednesday, Ada County Sheriff's Department spokeswoman Andrea Dearden said.

The rider didn't report his encounter with the pair until later, after seeing news reports and realizing they were being sought.

Idaho authorities started searching Thursday and the car was found Friday morning and identified through serial numbers as belonging to James Lee DiMaggio, 40.

There have been no other reported sightings of the pair since Wednesday, but the discovery launched a massive search in the southwest corner of The Frank Church-River of No Return Wilderness.

More than 100 people were searching on foot and on horseback or were on their way to join the search of an area that Ada County sheriff's spokesman Patrick Orr described Friday evening as covering 320 square miles.

The rider also told police it did not appear that the girl, believed to be 16-year-old Hannah Anderson, was being held against her will. Both people seemed healthy and were equipped with gear necessary to hike and camp in Idaho's remote wilderness.

"There was nothing that was so alarming at the time that he felt threatened or alarmed," Dearden said of the unidentified rider. "But after seeing the Amber Alerts, there was something that made him think, in hindsight, that it all seemed a little odd."

Brett Anderson, Hannah's father, said he was "very happy" that Hannah may have been spotted alive. He said he couldn't explain why his daughter didn't ask the horseback rider for help.

"We don't know what kind of frame of mind she was in or what he told her," Anderson said. "Maybe if she acted differently, there would be more dead people."

Hannah's grandfather, Christopher Saincome, also was relieved and refused to try to explain the girl's reaction.

"He could have strapped something to her and told her it was a bomb. He could have had her tethered to him," he said. "I'm sure she's totally in shock."

The car, a blue Nissan Versa, was covered in brush off a road about 5 or 6 miles from the spot where the man and girl had been seen. The license plates had been removed, but the vehicle identification number matched that of the car being sought, San Diego County Sheriff Bill Gore said.

Police previously warned that the car might be rigged with explosives. A law enforcement team from San Diego was expected to search and secure the car at the trailhead, sheriff's spokesman Orr said.

Morehead Lake is in the southwest corner of a rugged 2.3 million-acre preserve in the heart of Idaho. Because of its wilderness designation, the preserve is not open to motorized vehicles and traffic is limited to hikers and horseback riders - rules that will also apply to searchers.

The lake is about 2 miles west of the Middle Fork of the Snake River, a waterway that winds through the wilderness and is extremely popular for recreationists who float and camp for up to a week at a time.

The pine-blanketed area is at an altitude of about 7,800 feet and the lake itself is seven miles into the wilderness area. Temperatures at night can fall into the high 30s. Daytime highs can reach the 90s.

Police have set up check points in the area where the car was found and near other nearby trailheads, about 60 miles east of Cascade.

Gore noted that DiMaggio bought camping gear a few weeks ago.

Authorities throughout the West have been looking for the teen and DiMaggio since the bodies of the girl's mother, Christina Anderson, 44, and an unidentified child were found Sunday at DiMaggio's burned home near the Mexican border about 65 miles east of San Diego.

The unidentified body is believed to be that of Hannah's 8-year-old brother, Ethan. The body was badly burned and definitive identification hasn't been made.

DiMaggio was close to the family. Brett Anderson has described him as a best friend and said his children thought of him as an uncle.

Authorities have said DiMaggio had an "unusual infatuation" with the 16-year-old, although the father said he never saw any strange behavior. If he had, he said, "we would have quashed that relationship in an instant."

DiMaggio, a telecommunications technician at The Scripps Research Institute in San Diego, was planning to move to Texas and invited Christina Anderson and the children to his home last weekend to say goodbye, said Christopher Saincome, Anderson's father.

It's unclear how the two were killed, though police believe the crime was planned.

Brett Anderson said his friend is an outdoorsman.

"He was very interested in hiking and camping," Anderson said. "Whenever he had the chance and had the funds he would go on a hiking trip."

The Cascade area is an outdoorsman's paradise. Perched along the southeastern shoreline of the Cascade Reservoir and The West Mountains, the town is a popular summer getaway for hikers, campers and kayakers.