The surrounding ridges of Cushetunk Mountain endure because they were underlaid with dense and durable volcanic rock diabase that cooled slowly under the surface of the Earth.

The reservoir covers what used to be a farming community, with remains of a school and a church on the lake floor among other buildings.

[1][2] Reaching depths of 180 feet (55 m), this 2,350 acres (9.5 km2) reservoir is best known for its pristine clear blue waters.

The reservoir contains 55 billion US gallons (210,000,000 m3) of water for use in central New Jersey, making it the largest in the state.

The park also has a wilderness area for camping, swimming and SCUBA diving facilities, a boat ramp and nature hiking and biking trails.