Mt. Marshall is the most southern peak of the beautiful MacIntyre Range but unfortunately it is a bit removed from the next peak, Iroquois Pek, so it does not have any maintained trials to its summit. The clearest herdpath to the top is to follow Herbert Brook from the Flowed Lands just between the Flowed Lands and Lake Colden. You'll have great views up towards Colden on your trip to the base of Herbert Brook but unfortunately the summit of Marshall is wooded with limited views.
Upper Works Trailhead:
Take exit 29 off of I-87 and follow Rte. 2 for 17 miles to an intersection with a sign for "National Lead". Turn right here and after just half a mile you wil pass the intersection for the Tahawas Club and a sign for Lower Works Road before crosssing some railroad tracks. After 6.3 miles turn left onto Upper Works Road. The trailhead for Calamity Brook is at the very end of this road.
In the depth of winter you will probably be safe crossing directly across the lake on skis or snow shoes but in spring or summer you'll need to follow the gps track in this guide. You wil have great views towards Mt. Colden in the distance on the right.