Grassy Pond

click map for full-screen online map

Grassy Pond Map (PDF)

Location:  Northwest of Acton Center, between Nagog Hill Road and Newtown Road, toward Littleton

Loop trail:  1.1 miles

Acreage:  106.9

Terrain/Trail Conditions: Largely level from Newtown Road, including long boardwalk segment; from Nagog Hill Road slopes downhill toward pond; quite stony; trails occasionally wet in some places


  • Southwesterly side of Nagog Hill Road, 1.25 miles from Acton Center (Parking; Kiosk at end of meadow)
  • Northeasterly side of Newtown Road, west of Lincoln Road (P; K along access trail)
  • End of Willis Holden Drive, off Hammond Road via Samuel Parlin Drive

Grassy Pond and Nagog Hill Conservation Lands are contiguous properties, each with its own self-contained trail system. Together the two properties contain 273 acres within which a more than 3-mile circuit can be made by using the 0.2-mile red connector between the two trail systems. This connector leads into the Nagog Hill Conservation Land directly across Nagog Hill Road from the main Grassy Pond parking lot.

Grassy Pond Conservation Land comprises diverse habitats and ecosystems. These include the pond and its associated wetlands, two small streams, a vernal pool, a boulder field within moist woodlands, a large meadow, and forest vegetation of white pine, hemlock, and northern hardwoods. These latter include white ash, red and white oak, and some beech. In the spring, the white blossoms of dogwood trees may be seen scattered through the woods. Mosses are abundant in this moist forest, covering many stones and tree stumps.

This property’s trail system consists of a yellow loop trail that makes a circuit of the long rectangular upland portion, together with one blue crossover trail and three red access trails. The blue trail is a shortcut between two sides of the main loop and intersects the loop trail on its southerly side at the junction with the red access trail from Willis Holden Drive. The primary access trail enters from the Nagog Hill Road parking lot, passing through the northerly end of the meadow. The red access trail from Newtown Road is quite long and passes over a 425-foot boardwalk through a diverse red maple swamp at one of the pond’s two outlets, offering a view of the wetlands that is otherwise inaccessible. The trail then passes through a stand of northern hardwoods before connecting with the yellow loop trail close to the short blue trail leading to the pond.

Grassy Pond itself has formed in a kettle hole that resulted from the glaciers’ retreat; it exhibits bog characteristics around its perimeter. Nowhere is the pond more than 15 feet deep, although the level has fluctuated since the late 1990s due to beaver activity. The gradual invasion of the pond’s shoreline by plant species that thrive in very wet and highly acidic habitats will cause continuing shrinkage of the open water through an ever-quickening process of eutrophication. Leading this advance are pitcher plants, leatherleaf, highbush blueberries, larches, and red maples. A short blue trail off the yellow loop trail leads down to the water’s edge, where a wooden pier with observation platform reaches into the pond. Provided with benches and surrounded by bog species, this platform is open to excellent views and allows appreciation of the bog’s characteristics. Grassy Pond and nearby Nagog Pond, which is accessible from Nagog Hill Conservation Land, each demonstrates a different phase in the natural life cycle of ponds. Both are among the Commonwealth’s “great ponds” (defined by the state as “any pond or lake that contained more than 10 acres in its natural state”); they are the only two such ponds in town.

An understory plant that is prevalent on the Grassy Pond land is the vase-shaped witch hazel. Along the southerly side of the loop trail, there is a small grove of young hemlocks close to a fairly large vernal pool. The trail passes through the hemlocks and then skirts an impressive boulder field.

The large meadow adjacent to the Nagog Hill Road parking lot, kept open by seasonal mowing, contains several birdhouses suitable for bluebirds, which frequently nest there. The Grassy Pond land in general provides good habitat for many birds including pileated woodpeckers, which enjoy the hardwood forest. Owls, warblers, and other songbirds may also be seen. There is evidence of deer and coyotes, too. The many stone walls and remains of other stone structures speak of the historic uses of this area.

Grassy Pond Map (PDF)

Grassy Pond Map (full-screen online map)