DENNIS HILL STATE PARK
Hike to the summit of this 240-acre estate for panoramic views reaching as far away as New Hampshire. Fall foliage season makes Dennis Hill an autumn wonderland.
A gently sloping road leads to the top of Dennis Hill. This description of the geology starts with a walk up the road. Follow the road when it bends to the right, and the yellow trail branches off. Look for a low outcrop below a stone wall.
The rock here is a medium grained, medium gray gneiss with a fold in it. Although the rock formation in this part of the park is described as schist, here the rock has less mica, and can be called gneiss.
The next outcrop, on the right after passing a grassy parking area, is nearly flat and has glacial striations (parallel grooves) on its surface (Figure 2). The striations were caused by frozen rocks at the bottom of the glacial ice that ground across the rock surface as the ice moved south. Glaciers covered Connecticut at least two times, the most recent from about 25,000 to 15,000 years ago.
This outcrop of schist (a rock containing lots of mica) has tiny crinkle folds barely visible in the western side of the rock. Gray, quartz veins cut through the east side. Continuing on around the curve, find another nearly flat outcrop. This one has a quartz vein, about one-foot wide, running through it.
A little more walking brings you to the top of the hill, and a very large outcrop surrounded by grass. Here, you get a great view of how much this rock has been deformed over time by continental collisions. Rock can actually fold when buried, heated deeply in the Earth, and under a lot of pressure. Many miles of rock sat above the surface you are now walking on. All of it was eroded away over millions of years.
Climb the tower on the pavilion to look at the wonderful view. On an average clear day you can see at least three states, more if the air is exceptionally clear. Walk back down the road to the grassy parking area where the white trail begins. Follow it. Soon you will walk over an outcrop of folded schist (Figure 5).
Continuing on down the white trail, look for a large outcrop on the left. This rock is fine-grained, dark-gray gneiss with a steeply dipping face (Figure 6).
At the end of the white trail, turn right onto the yellow trail. When the trail branches, follow the right branch. Soon you will reach a nice overlook with a circular stone wall, a stone, and a wooden, picnic pavilion. (Figure 7).
Continuing on the yellow trail, there are few outcrops until just before the point where the trail loops back toward the south. A low, steep outcrop with distinct flat, vertical faces there is made of quartzite. This rock probably started out as a sand beach, was gradually changed to sandstone, then under high pressure, and heat, recrystallized to quartzite (Figure 8).
Head back toward the parking lot on the yellow trail you already traveled, when it completes the loop. After passing the white trail, notice a small quarry that has been cut into the gneiss on the right. (Figure 11). Look for short, drill holes, the kind made with a hand drill and mallet. These holes are smaller, and shorter than those used for dynamite. There are several areas of tumbled down rocks along this section of the trail, but it seems that only one contains drill holes. Maybe you can find some in other areas.
Dennis Hill, a 240-acre estate, was gifted to the State of Connecticut in 1935 by Dr. Frederick Shepard Dennis, a noted New York surgeon. A unique summit pavilion (formerly summer residence), located at an elevation of 1627 feet, is a popular attraction. Haystack Mountain, Mt. Greylock, the Green Mountains, and a portion of the State of New Hampshire can be seen from the summit in clear weather.