Round Mountain, 780 feet (238 m) above sea level, was a peak of the Holyoke Range of traprock mountains located in the Connecticut River Valley of Massachusetts, and part of the greater Metacomet Ridge that stretches from Long Island Sound nearly to the Vermont border.

Round Mountain was located mostly within Granby but some land was within the towns of Amherst and South Hadley, Massachusetts.

The rocks forming the mountain were extruded near the end of the Triassic Period when North America was rifting apart from Africa and Eurasia.

Subsequent faulting and earthquake activity tilted the strata, creating the dramatic cliffs and ridges of Bare Mountain.

Hot, dry upper slopes, cool, moist ravines, and mineral-rich ledges of basalt talus produce a combination of microclimate ecosystems on the mountain that support plant and animal species uncommon in greater Massachusetts.