Diamond Peak is in the 4th highest peak in Idaho and the highest in Idaho's Lemhi Range. It is also one of the world's Ultra Prominent Peaks (1500 m prominence).
Despite a long, bumpy drive to a pretty high trailhead, the route still raises 4000 feet in under 3 miles, which would qualify it as a vertical kilometer route according to vertical kilometer race standards.
The route begins on an unmaintained, but well worn, trail and then continues as a Class 3 or less scramble on the upper flanks of the mountain in the last mile or so. The scramble portion of the route is easy to follow and is never exposed. The route is out-and-back, so just head straight back down the way you came.
At the top, the views of Eastern Idaho are expansive! More mountain, route, and approach information can be found on SummitPost: https://www.summitpost.org/mountain/152083.