The Elkhorn Crest is the highest elevation singletrack trail in eastern Oregon. You'll need a high clearance vehicle to drive to the trailhead or you can park as far up as you can go and ride your bike from there.
There are lots of mountain goats on the Elkhorn Crest Trail and it is great as an out and back to Columbia Hill. If you're looking for something a little easier, there are a couple of shuttle options that can be pieced together. The first 5 miles to the Twin Lakes Trail intersection is a blast both out and back. From 5 miles to 8 miles is rocky and has significant exposure -- but it is all rideable and fun. From 8 miles to 14 miles is great singletrack, there are some rocks but it's mostly fast and technical trail.