Pinnacle Rock is a 600-foot traprock peak on the Metacomet Ridge in Farmington and Plainville, rising prominently above the upper Quinnipiac and Farmington river valleys and offering broad western views. Part of a long ridge system stretching from near Long Island Sound to the Vermont border, it was formed from basalt laid down near the end of the Triassic Period and later tilted by faulting and earthquakes. Its varied geology supports uncommon plant communities and makes the ridge an important route for migrating raptors. A popular outdoor destination crossed by the Metacomet Trail, it has also faced development and quarrying pressure and briefly hosted a Cold War Nike missile base.