It is part of the Metacomet Ridge that extends from Long Island Sound near New Haven, north through the Connecticut River Valley of Massachusetts to the Vermont border.

The summit is open with a 360° view encompassing Long Island Sound, the Quinnipiac River estuary, New Haven Harbor, and the surrounding peaks of the Metacomet Ridge.

The mountain formed near the end of the Triassic Period with the rifting apart of the North American continent from Africa and Eurasia.

Subsequent faulting and earthquake activity tilted the strata, creating the cliffs and ridgeline of Peter's Rock.

Of particular note is the large, well-defined columnar basalt formation on the southwest side of Peter's Rock.

Hot, dry upper slopes, cool, moist ravines, and mineral-rich ledges of basalt talus produce a combination of microclimate ecosystems on the mountain that support plant and animal species uncommon in greater Connecticut.