Rolling through southwestern New Hampshire in the heart of New England, the Ashuelot River has a drainage basin encompassing nearly 420 square miles. In its approximately 64-mile journey spanning from the towns of Washington to Hinsdale, the Ashuelot affords areas with both cultural and environmental significance. The river boasts the site of the oldest known evidence of man in New Hampshire, dating back 10,500 years, and has also been identified by the US Fish and Wildlife Service as one of the four most important refuges for the federally-listed endangered dwarf wedge mussel. The Ashuelot became recognized as a state-designated river in June 1993.

The Ashuelot River watershed is included in the Silvio O. Conte National Fish and Wildlife Refuge Act. The Act was passed in 1991 to conserve, protect and enhance the diversity of species that exist within the entire Connecticut River watershed. The US Fish and Wildlife Service, which administers the program, has identified special focus areas throughout the watershed where resources are deemed highly valuable. The upper reach of the Ashuelot River is one such focus area, recognized for the rare dwarf wedge mussel and fine fishery supported there. The agency will direct its efforts toward the protection of these sites through various programs, including environmental education and habitat management.

The headwaters of the Ashuelot River begin in Pillsbury State Park at an elevation of approximately 1,600 feet. From there the river drops at a rate of 37 feet per mile over the first 30 miles, creating a steep gorge with numerous waterfalls in Gilsum. Several potholes, including Devil’s Chair, are also located in this reach of the river. Throughout the river corridor, there are remnants of past glacial activity including varved clay deposits, deltas, drumlins, and glacial Lake Ashuelot. Also of interest are the many quarries in the area producing sand, gravel, and semi-precious stones, and the high potential aquifers found in the river corridor.