Pioneer Valley - Geology

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, lending it much of its picturesque beauty... 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.