Lying face-down in a drainage area of French Pete Creek in the Three Sisters Wilderness, half of a trail guide book provided the first clue in the search for a missing University of Oregon professor.

The first half of the book, from the front cover to page 157, was open to the Olallie Mountain area where the professor went missing.

Searchers found the second half of the book in Daming Xu's car, located at the trailhead early on.

KGW photos

Daming Xu and his car, which was found at the trailhead.

An independent hiker working in cooperation with the Lane County Sheriff's Office found half of the book late Tuesday, about eight miles from where Xu was last seen by a couple hiking Olallie Mountain.

A team of volunteers from Eugene Mountain Rescue entered the drainage Wednesday but were unable to find additional clues, according to Sheriff Russel Burger.

A focused search in the drainage area continued Thursday. Due to the remoteness and ruggedness of the area, only trained searchers were involved.

They started at French Pete Creek and Forest Road 19, south of the Cougar Dam reservoir, working on the theory that professor Xu had followed the creek downstream from where the book was found.They had previously searched upstream from French Pete Creek to an old airstrip along Olallie Trail.

Thursday's search also failed to turn up any additional clues.

Background: Found footprints turned out to be false alarm

The search was scaled back Monday and crews described it as a “recovery” effort.

More: Search crews fear the worst

Xu has been missing since November 4th. His car was found at the trailhead early on in the search.

The mathematics professor had embarked on a day hike and was believed to be lightly dressed and without food or water.

Lane County Sheriff Search and Rescue coordinator Lt. Randy Smith said he does not believe Xu could still be alive.

Also: Grandmother found alive after 13 days lost in wilderness

Last summer, a grandmother from Sandy, Ore. was found alive in the Wallowa Mountains after missing for 13 days.