Round Mountain was a 780-foot traprock peak in the Holyoke Range of western Massachusetts, mostly in Granby and partly in Amherst and South Hadley, that helped form the narrow passage called the Notch with Bare Mountain. Long used as a Native American footpath, then a dirt road, trolley route, and later Route 116 corridor, the gap was once far more dramatic before quarrying reshaped the landscape. Formed from basalt lava near the end of the Triassic Period and later tilted by faulting, the mountain also supported uncommon microclimates. Mining that began in 1897 has nearly erased it, leaving Round Mountain chiefly as a geological and historical reference.