The pickup belonging to Suzanne Durheim, reported missing on Monday, was towed out of the Willamette River near Corvallis shortly after noon on Wednesday.
But authorities did not find the 66-year-old Brownsville woman.
"We've got our marine boats out there searching, and we're going to continue, but it's going to be difficult," said Benton County Undersheriff Greg Ridler on Wednesday afternoon.
"The main focus for us is helping the family know what happened. We still can't do that, so it's frustrating," he added.
Public safety workers didn't locate Durheim before they suspended operations due to nightfall on Wednesday, but the Sheriff's Office planned to have patrol boats with sonar and a dog searching for her on Thursday.
However, a body in the Willamette River could potentially remain submerged for days and resurface miles downstream, Ridler noted.
Durheim's pickup was located by the Benton County Sheriff's Office and the Linn County Sheriff's Office on Tuesday afternoon, but the tow was pushed back to Wednesday due to complications.
The vehicle came to rest in the river by the Hewlett-Packard campus on Highway 20.
AA Towing and B&R Towing both helped to remove the maroon 2003 Ford F-150. The pickup was pulled partially from the water, but it was sideways, so authorities repositioned the rig so it could be dragged backward up the steep embankment, which was filled with brush.
"I was skeptical they were going to be able to get it up that steep incline," Ridler said.
Traffic was restricted to one lane on Highway 20 during the tow operation.
An examination of the truck on Wednesday afternoon didn't reveal clues as to what might have happened to Durheim.
Durheim was reported missing by her family shortly before 2 p.m. on Monday after she didn't show up for work that morning at Samaritan Health Plans.
Her family then followed the routes she would have normally taken to work, and found a piece of her fender along the highway.
Authorities responded to search the area until 7 p.m. on Monday, then resumed the search with water dive teams and patrol boats on Tuesday.
The crash may have occurred after 6 a.m. on Monday, when many roadways in the mid-Willamette Valley were slick due to low temperatures. Police believe that Durheim may have slid off the icy highway and into the river.