Mount Greylock is like an island, different in geology, climate and ecology from its local surroundings. Rising above the region one can view the neighboring Taconic, Hoosac, and Green Mountains and Berkshire Hills, and further in the distance, the Catskills, Adirondacks and White Mountains.
The Reservation includes the promontories Mounts Prospect, Williams, and Fitch, Saddleball, Ragged Mountain and Stony Ledge, as well as Mount Greylock summit. The Hopper, surrounded on three sides by steep slopes, is a unique geologic valley supporting stands of old-growth red spruce forest over 150 years old. The Society of American Foresters designated the Hopper a Natural Area in 1978, followed in 1987 by the National Park Service designation as a National Natural Landmark.
Ecologists have compared the transition in forest vegetation zones from base to summit as if walking from Pennsylvania to northern Maine in one day. Quite aptly, William Brewster, an eminent 19th century ornithologist described the mountain as “a Canadian island rising from an Alleghenian sea.” The Northern hardwood forest is found on the lower slopes: Red Oak, beech, birches, Black Cherry, ashes and maples. At about 2,600 feet in elevation this transitions into the boreal or spruce-fir forest dominated by Red Spruce and Balsam Fir, joined by Mountain Ash and Yellow Birch; the only sub-alpine environment in Massachusetts and southern New England. Due to the higher elevation spring flowers can often still be found blooming into early summer throughout the reservation.
The backbone of the mountain was formed from the remnants of an ancient sea bed. According to geologists, between 600 to 450 million years ago, the older Greylock Schist and quartzite formations of mountain are believed to have been thrust up and folded over on top of the younger limestone and marble of the Hoosac Valley to the east. At one time reaching perhaps 20,000 feet in height, the Greylock massif has been reduced to its present size over eons by constant erosion, a process that still continues, and on the rare occasion in the form of a landslide.
Between extreme changes in climate, topography and ecology, the mountain provides some unique habitats that support a wide variety of animals. One may find here almost 100 species of birds including thrushes, sparrows, warblers, game birds, hawks, owls and ravens. Mammals commonly include: moose, white-tailed deer, black bear, bobcat, coyote, red and gray fox, fisher, porcupine, beaver, raccoon, snowshoe hare, woodchuck, red and gray squirrel. Habitat restoration programs by MassWildlife in two locations, Jones Nose and Haley Farm, seek to improve biodiversity of animal species and control exotic invasive plants.