Lost River Mountain is 12,078 feet high and number 6 of the 9 highest 12k mountains in Idaho. This is steep the whole way up and down with lots of sliding near the top because of the angle and loose rocks. The visible top from the trailhead or highway 93 is not the actual summit, there is a short ridge walk north from there.
Tough hike, but worth it (and required if you are looking to get all 9 of Idaho's 12,000+ feet mountains). For me this is the 4th 12er I have done so far, the others being Borah, Leatherman, and Hyndman.