festivals that draw millions of visitors, such as The Big E—all six New England states' collective, annual state fair in West Springfield—and Bright Nights at Springfield's Forest Park—an elaborate, high-tech lighting display during the holiday season. Geology The Pioneer Valley includes approximately half of the southern Connecticut River Valley—an ancient rift valley created by the breakup of the supercontinent Pangea along the Mid-Atlantic Ridge during the Triassic and Jurassic periods of the Mesozoic Era. The Connecticut River has been flowing through the valley for millions of years and was naturally dammed to form glacial lake Hitchcock during the last ice age. According to King's Handbook of Springfield, by Moses King, the Pioneer Valley "is not an ordinary river channel; it is, in fact, a trough between two systems of mountains. To the west lie the worn-down remnants of the once lofty Berkshire Mountains; on the east, the yet more degraded ridges which constitute what we may call the Eastern Massachusetts set of mountain ridges. These rocks now form many sharp hills and mountains in the Valley. During the Triassic time, Massachusetts's portion of the Connecticut River Valley formed a shallow arm of the sea," leaving deposits that enriched the Pioneer Valley's inordinately fertile soil. Geologically interesting parts of the Valley are the basalt flows and dinosaur tracks in South Hadley and Holyoke, Massachusetts, a chain of basaltic traprock ridges known as Metacomet Ridge along the ancient tectonic rift including the Mount Holyoke and Mount Tom ranges, layers of rock deposit laid down by the river, and varves and deltas deposited by Lake Hitchcock during the Pleistocene. Political geography The region known as the Pioneer Valley constitutes Massachusetts's portion of the fertile Connecticut River Valley and the hill and mountain towns to its east and west. The following three counties—from north to south, and each with a different character—encompass the Pioneer Valley: Franklin County Franklin County is the most rural county in Massachusetts and thus reminiscent of southern Vermont, which it borders. Greenfield is its largest municipality, a small city frequently used as a gateway to the region's many outdoor pursuits. The county offers downhill skiing at resorts such as Berkshire East, white-water rafting, zip-lining, hiking, kayaking, and other outdoor pursuits. In addition, Franklin County contains many rustic, former mill towns. Many of these have become quaint and scenic since the decline of the mills (e.g., Turners Falls). Massachusetts's Routes 2