My experience with Hwy 299 leads me to believe they won't find Jeff's car at all, hidden or otherwise. Here's why:
Back in 1978 my ex and I were heading home to Seattle from Long Beach, CA. We had driven up I-5 and decided to take 299 over to the Arcata/Eureka area, so we could drive up the Oregon coast and stop to see my folks.
It was springtime and there'd been a lot of rain. We were driving through the twistiest bits of the highway, that runs right along the edge of the ravine down to the river. At that time, there was no shoulder at all on either side of the road. The westbound lane was bordered by cliff face to the north, and the eastbound lane had a sheer dropoff to the south. So, we're tooling along and all of a sudden a HUGE rock (visualize about the size of a 25 pound turkey) comes bouncing down the cliff face and lands on the road in front of us, and broke into two pieces. There was no possibility to slam on the brakes in time, or swerve to avoid it without going down the embankment to the river, so the ex drove over the two pieces of the rock, and came to a stop as safely as possible, trying to avoid being rear-ended by a car behind us. Fortunately the only thing hurt was the car, and the folks behind stopped and gave us a ride to Eureka. Once we got there, we called the Highway Patrol to let them know about the car and we were told to hire a tow truck ASAP and get back up there to get our car, because it wouldn't be there in the morning. They told us the reservation land up there was notorious for bad things happening to people and their cars, and our car would be stripped and sold for parts within 12 hours if we didn't go back immediately and get it.
So my thought is Jeff's car was not hidden, it was parted out and sold.