Long Mountain is a prominent traprock ridge in the Holyoke Range of western Massachusetts, spanning Amherst and Granby and forming part of the larger Metacomet Ridge. Though only 920 feet high, it rises sharply above the Amherst area and Fort River valley, with five distinct peaks and broad summit views. Its basalt was laid down near the end of the Triassic Period as North America began rifting from Africa and Eurasia, then later tilted by faulting and earthquakes. This geology created diverse habitats uncommon in much of Massachusetts. Long Mountain is also a popular recreation area, with major trails crossing land protected by the state, local conservation commissions, and private owners.