CHAPTER 3 Natural Resources long the Mohawk Trail Scenic Byway lies a wealth of important natural resources. Among these resources are: the Deerfield and Hoosic Rivers, which contain important trout habitat; the Glacial Potholes in AShelburne Falls, one of the largest collection of such potholes in the country; the Natural Bridge in North Adams, the only bridge in North America created by the erosive forces of water; and miles of northern hardwood forests along the Byway corridor, including old growth forests in the Mohawk Trail State Forest. The Byway also includes other geologic, flora and fauna, water resources that help make the Mohawk Trail Scenic Byway experience unique. The corridor’s natural resources contribute to the dramatic scenery viewed from the Byway, and attract recreational tourists seeking to experience the corridor’s wildness. This chapter of the Corridor Management Plan provides a gen- eral inventory and overview of the Byway’s natural resources, in- cluding its geology, soils, water resources, and rare species habitat areas. The purpose is to highlight the Byway’s primary natural and environmental assets. The chapter also discusses potential issues that could affect the quality of these resources over time, especially if the Byway experiences an increase in tourist and vehicle traffic. The chapter closes with a series of recommendations for protect- ing, maintaining, and enhancing the Byway’s natural resources. ago, a period of mountain building Geologic Resources (also known as an orogeny) called the Taconic Orogeny created the Taconic Geologic History Hills of western Berkshire County. During this period, bedrock and sedi- The formation of the Byway landscape ment deposits of the warm sea were began approximately six-hundred mil- pushed westward and inland. lion years ago. During that time, the During a second period of mountain region now occupied by Berkshire and building, the Acadian Orogeny, the Franklin Counties was located south earth’s crust was thrust westward ever of the equator, and lay submerged at further, creating the northern Appala- the tropical edge of North America chian Mountains. Rocks from a dis- under the warm sea that preceded what tance away were folded up against the is now the Atlantic Ocean. Over the already existing rocks, buckling like a next several hundred million years, the rug. Entire rock formations fractured processes of plate tectonics pushed and cracked, creating shear zones run- several land masses into the eastern ning north-south along Berkshire edge of North America, creating new County. Older ocean bedrock was mountains with each impact. Begin- thrust upward over younger rocks also ning approximately 500 million years derived from ocean sediments. The ef- 26 MOHAWK TRAIL SCENIC BYWAY fect of these stresses was to transform Geology Today the tropical marine sedimentary layers Traveling along the Mohawk Trail to- into metaphoric rocks, including day, the region’s varied geology can be 1 gneisses, schists, and slates. Today, seen from a number of locations. Leav- 2 caps of phyllite and schist protect the ing Greenfield, traveling west, the By- Taconic Hills, and caps of schist and way begins a long ascent around gneiss cover the Berkshire Highlands. Greenfield Mountain. The man-made Softer limestones, marble, and dolo- Longview Tower, located along this mites (which resemble limestone) are climb, provides scenic views of the folded in amongst these harder rocks. Connecticut River Valley and its geo- The Connecticut River Valley, to the logic past. To the east of the tower, lies east of the Berkshire Hills, was formed ridges of dark grey volcanic rock in the approximately 200 million years ago, af- valley, and near the tower, roadcuts re- ter the Taconic and Berkshire Hills. The veal an outcrop of schist. West of the Connecticut River Valley was created as tower, the Mohawk Trail travels preexisting rocks in the region stressed around the north side of Greenfield and pulled apart, opening up a fault be- Mountain, which is comprised prima- tween the rocks. Rivers washed large rily of gray Gile Mountain schist and amounts of sediment into the Connecti- metamorphic amphibolites, made up cut River Valley; in the Greenfield– of minerals rich in iron, calcium, and Montague part of the Valley, about 6,000 sodium (Skehan, 2001). feet of sediment remain today. As with Between Greenfield and Charlemont, the hills to the west, the Connecticut the Mohawk Trail crosses over complex, River Valley ridges initially grew as folded schists. Gneiss forms the core of stresses pushed rocks upward, and then the Shelburne Falls dome, and of the gla- softened as glacial movements and cial potholes located below the Salmon weathering eroded the Valley’s edges. Falls. The potholes in Shelburne Falls are The mountain ranges created during the one of the largest known concentrations ancient mountain building periods are of glacial potholes in the country. The believed to have once been 20,000 feet more than fifty potholes, ranging in size high. However, the combined effects of from six inches to thirty-nine feet, were weathering, river systems, and glacial formed by the whirlpool action of water movement have softened these moun- and gyrating stones during the glacial age. tains into hills that are now generally They were created beginning 14,000 years 2,000 to 3,000 feet high. Also, over time, ago, when flooding and receding waters mountain streams have carved sharp ra- of the Deerfield River eroded the under- vines through bedrock faults running lying gneiss rocks, and have continued to down the harder metaphoric rocks form and change ever since. (phyllites, schists and gneisses) that Traveling from east to west along the make up the ridges along the Byway. Byway between the Charlemont fault and Whitcomb Summit, one passes 1 Gneiss is a light and dark, medium to coarse- grained metamorphic rock characterized by through three distinct geologic forma- compositional banding of light and dark min- tions, all of which can be seen from the erals. Schist is a light, coarse to very coarse- roadway. They are the dark green grained, strongly to very strongly layered metamorphic rock whose layering is typically Hawley volcanic rocks, the gray defined by parallel alignment of micas. Slate is Moretown schist, and the emerald a slightly metamorphosed shale or mudstone green Rowe schist (Skehan, 2001). that breaks easily along parallel surfaces (Skehan, 2001). Moving further west along the Scenic 2 Phyllite is a metaphoric rock intermediate in Byway, one sees Hoosac schist from the grade (and grain size) between a slate and a West Summit Overlook, and at the schist(Skehan, 2001). CHAPTER 3: Natural Resources 27 Ice clings to the Hoosac schist seen at the Hairpin Turn, Florida. Hairpin Turn on the Clarksburg-North provided numerous opportunities for Adams town border. To create the road- the mining of marble and limestone. Sev- way here, several hundred feet of bed- eral marble and limestone quarries once rock were blasted open, exposing the thrived throughout Berkshire County, thin layers of schist with scattered veins and Specialty Minerals Inc. continues to of quartz. This rock was formed from mine limestone in Adams today. One sediment deposits laid upon the conti- fine example of an abandoned marble nental shelf of ancient America. mine can be seen at Natural Bridge State The ancient Hoosic River carved a Park, in North Adams. The quarry is ad- valley through the softer marbles and jacent to the Natural Bridge, a geological limestones at the western end of the formation which is the only bridge in Byway. Glacial ice smoothed the hills North America created by the erosive and widened the river valley, grinding, forces of water. The exposed bedrock mixing and depositing debris as suc- near the bridge is Stockbridge marble, a cessive ice sheets advanced and re- light grey stone that was formed over treated in a north-south direction over 500 million years ago. The bridge itself, many thousands of years. Shore depos- however, is estimated to be only 10,000 its from a large glacial lake that once years old, and was created during the last submerged the Hoosic and Green Ice Age. In the past, Hudson Brook, River Valleys, and from more recent which previously ran higher and stron- flood deposits from the rivers them- ger, carved out a 475-foot long by 60- selves, have left rich alluvial soils along foot deep chasm through the marble. the valley floors. A patchwork of agri- The brook flows easier now, having cultural fields still exists along the carved only about one extra foot deeper wavy hills and lowlands of the valleys, in the last 8,000 or 9,000 years (Plante, as one can see from several vantage 2000). The brook also sculpts potholes points along the Byway. in the marble as the water swirls down- The softer deposits that once lay on ward. The 30-foot Natural Bridge and the floor of the ancient warm sea later associated walkways offer “an intimate 28 MOHAWK TRAIL SCENIC BYWAY yet safe look at the tremendous power of flowing water” (Laubach, 1992). Soils The characteristics of the different types of soils along the Mohawk Trail Byway dic- tate the type of activity and development that can reasonably take place there. The soil types found along the Byway corridor occur in natural groups know as soil asso- ciations. This section provides an overview of the soil associations found along the By- way, traveling from east to west. The Colrain-Buckland Association is the major soil group along the segment of the Byway between Greenfield and the Deerfield River. These soils are generally shallow to bedrock, rocky, and moder- ately acidic. They are present on rolling to steep hills, are moderately to very perme- able and loamy, and are often stony.