The Pawtuckaway Mountains in New Hampshire are a small, rocky, circular range. They form the outline of an ancient volcanic ring dike, dating from 130—110 million years ago (Cretaceous era).
Pawtuckaway State Park is in Nottingham, New Hampshire.
The summit of South Pawtuckaway Mountain, seen from the fire tower.
The ring dike is a smaller and more accessible example of the same kind of geological process that formed the Ossipee Mountains to the north. The inner ring is roughly one mile in diameter, while the outer is measured at almost two miles.
If you are flying overhead, an aerial view clearly shows the ring:
Earthquakes occurred in the vicinity of the ring dike in the summer and fall of 1845. Known as the Deerfield explosions, they were described as subterranean noises often as loud as the report of a 12 pounder cannon when heard at a distance of half a mile but without echoes. They were the subject of much speculation at the time.
Topographical map of the area.
Illustrations here are taken from “The Geology of the Mt. Pawtuckaway Quadrangle New Hampshire”, Jacob Freedman, New Hamp. State Planning Development Committee, 1950. Revised by Michael Noetzel, “Nashuan”.
Visiting the park
Pawtuckaway State Park offers a variety of landscapes, with something to do and see for everyone. The park includes a large family beach on the lake. There are many opportunities for hiking, with trails leading to many special points of interest, including a mountaintop fire tower; an extensive marsh where beavers, deer, and great blue herons may be seen, and a geologically unique field where large boulders called glacial erratics were deposited when glacial ice melted near the end of the Ice Age.
Other Volcanoes in New Hampshire
New Hampshire Geologic Survey publications
Bulletins with maps, maps, subject reports and Fact Sheets. Publications can be found using one of three methods below:
NH Geological Survey Publiations