Photos from this trip can be found here.
Koppen Mountain marked last of the Mountaineers Teanaway 20 peaks pursuit. We started from the Boulder DeRoux trailhead, crossed the bridge, and got to the first trail junction. Then we took the Middle Fork Teanaway Trail and followed it all the way to the pass. We made a left on the pass and started traversing southeasterward via northwest ridge.
We followed a faint hikers path all the way to the summit. The path became more definite higher up.