Beginning at the Georgetown Circle Trailhead, take the short spur to the river and turn south (right). Here the river is slow moving, with broad pools bordered by hemlocks, red maple, beech, birch, oak, and a good understory of laurel. Very soon, the river is divided by long, narrow Ivy Island into two beautiful streams. Here the river drops over a long stretch of rocks and ledge. Several log crossings allow access to the island. Below the island the trail passes through hemlock glens, now under stress from hemlock wooly adelgid attack.
The east bank, which is often higher, affords good views of moss-covered rock outcrops and of flowing streams and seeps that add color and contrast, especially in winter.
Downriver, several small islands create more divisions in the river. Indeed, at one point the trail crosses a series of bouldered washes that at high water times create a series of temporary islands.
Eventually, the trail ascends a slight rise and passes through and then along a fine stone wall. Along this stretch and elsewhere, the bark of the beech trees appears cracked. A close look will reveal white, wax-covered colonies of the introduced beech scale. The fissures on the beech tree are the result of past feeding by heavy populations of this tiny sucking insect.
Where the wall ends temporarily, look for the large hemlock and the magnificent chestnut oak with its deeply fissured bark. Soon the trail crosses Cider Mill Brook on a footbridge. Just south of the bridge is the junction of the Cider Mill Brook Spur Trail (described below) that leads west and then north to Trailhead 3 on Concord Drive.
Continue south, through a stretch of hardwoods with an understory primarily of beech and laurel. Just south of another stone wall crossing, the river narrows and drops over a series of beautiful rapids. A few yards further are the foundation remains of a dam with its stone opening to a mill’s flume; see “Historical Features” below). Cross the head of the flume and follow its wall 160’ to the mill site itself .
Below the mill, the river continues to flow rapidly, with alternating pools and cascades. Large hemlock, beech, red maple, black birch, oak and occasional tulip poplar, sycamore, and yellow birch line the river banks. Stone walls reveal old field borders and property lines.
Just below where a small stream drains a valley to the west—and where the river makes a sharp bend—the trail crosses another bouldery wash which, in flood times, becomes a flowing stream creating a temporary island similar to those described earlier. The Trail crosses the outlet to the wash (shown as the southernmost stream crossing on the map). Just below this point, the trail enters private land and then soon after leaves the river along a stone wall to Trailhead 4 on Summer Hill Road.
From Trailhead 3, follow along the trail bordering a wet drainage through a forest of beech, red maple, ash, tulip-poplar and black and yellow birch. The wet swale soon meets the Cider Mill Brook flowing south. The trail essentially follows—at a distance—the west bank of the brook. Note the high ledges to the west. Eventually, where the trail passes through stone walls (the second of which opens into a crossroads of woods roads), turn sharply left, closer to the brook, and follow it to its junction with the main river trail.
Approximately 1.2 miles south of Trailhead 2, the remains of a mill exist on the west bank of the river. The site is approximately 0.8 miles north of Chestnut Hill Road and is easily reached from Trailhead 4. These foundations and structures may date from December 16, 1720, when five men were granted permission to erect a saw mill on the river between Hog Pond Brook and Ivy Island. Later maps also show a saw mill at this site.
The hiking trail runs between this mill and the river. Steps descend and rise on either side of the channel where water exited the mill. A walled area approximately 9’ deep may have been the area for the saw. Above the mill a flume, or raceway, runs approximately 160’ north to remnants of a dam. This structure diverted water to power the mill. The “outer” walls of the flume, those closest to the river, are approximately 6’ high and 5’ thick.