Hadley Mountain is a popular hike which though short in distance at 1.8 miles, achieves a sharp elevation gain of 1525 ft. The summit offers outstanding views of the Southern Adirondack Mountains and especially the Great Sacandaga Lake. The only trail begins from the trailhead parking area next to an Historic Marker and begins an immediate climb. The hiking register is reached within a couple of dozen yards of leaving the trailhead. A moderate climb following red trail markers leads through woodland on a mostly bedrock trail. Crossing back and forth over a small creek (dry in summer), the trail continues steeply past interesting boulders and cliffs to a level shoulder at about 1.0 mile. Following this brief gentle section the trail steepens and continues mostly on bedrock to the summit. Outstanding panoramas can be viewed from clearings along the final 0.5 mile to the summit, and from the summit itself.
At the summit, a firetower affords a commanding 360 degree panorama, taking in Great Sacandaga Lake, the surrounding southern Adirondacks and the High Peaks of the Adirondacks.
Descent is via the same trail.
The summit of Roundtop Mountain may be reached via a 0.8m bushwhack from the summit of Hadley Mountain by heading NNE. In Winter this is a popular snowshoe trail due to access and length of trail to summit.