Mount Nonotuck, an 827-foot peak in Holyoke and the northern end of the Mount Tom Range, rises sharply above the Connecticut River Valley as part of the Metacomet Ridge. Known for its rugged profile, broad views, and the Metacomet-Monadnock Trail, it also preserves traces of a summit resort era. William Street opened Eyrie House there in 1861, and its rivalry with a hotel on Mount Holyoke spurred improved access across the river. After a fire destroyed Eyrie House in 1901, its ruins became part of the Mount Tom Reservation. The mountain’s basalt cliffs, formed through ancient lava flows and later faulting, also support unusual habitats.