The Metacomet Ridge extends west from East Rock as series of smaller, unnoteworthy traprock outcrops to West Rock Ridge; it extends east over another series of traprock outcrops to Saltonstall Mountain and Peter's Rock. The west side of East Rock drains into the Mill River thence to New Haven Harbor and Long Island Sound; the east side into the Quinnipiac River, thence to New Haven Harbor and Long Island Sound. Both rivers abut the base of the mountain.