A cache by SuretteFam Message this owner

Hidden : 3/3/2026

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Size: Size: other (other)

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Geocache Description:

Welcome to one of the finest examples of geology in Cape Ann– the Monoliths!

Geology of Cape Ann

An Ancient Foundation

The bedrock of Cape Ann is among the oldest in New England, formed roughly 450 million years ago during a period of intense volcanic activity. Molten rock cooled slowly beneath the Earth’s surface, eventually becoming the distinctive Cape Ann granite. Over time, tectonic collisions and continental shifts pushed this rock upward, locking it in place as a durable foundation.

This granite is famously hard and weather-resistant, which is why Cape Ann’s coastline looks so bold and angular compared to softer, sandy shores farther south.

How did these massive boulders get to Cape Ann?

While the granite formed deep underground, glaciers were the forces that sculpted it into its present shape. During the last Ice Age, massive ice sheets advanced and retreated over Cape Ann, grinding the surface like sandpaper. As the ice moved, it carved smooth domes, deep grooves, and striations (deep scratches) that are still visible today at places like Halibut Point, Straitsmouth, and Thacher Island.

The glaciers also plucked and transported enormous boulders, depositing them as glacial erratics—rocks that seem oddly out of place but serve as clear evidence of ice-driven movement. The Monoliths are spectacular examples of this phenomenon.

Marks left behind by the glaciers on the high peaks of the Adirondacks and New England mountains tell us that the glaciers covered the tallest peaks in the Northeast, reaching a thickness of between one and two kilometers (0.6 to 1.2 miles). Even during this time of glacial advance, however, the ice sheet was always melting at its fringes, shaping the landscape at the glacial front (known as the periglacial zone).

The Monoliths

The Monoliths lie in a 146-acre park in Manchester-by-the-Sea, owned by the Trustees of Reservations. According to the Trustees’ website, and the identical sign at the trailhead:

“The Big and Little Rocks are dramatic examples of giant boulders plucked from bedrock and carried far away by the last glacier. As the glaciers scoured this landscape, the mass of bedrock forming the hill proved more resistant than the surrounding soil, forcing the bottom of the glacier up and over the hill. The north side was smoothed and the south side left steep and rugged as the glacier broke off chunks of rock as it passed.”

Big Rock in November, 2025

Little Rock in November, 2025

The Monoliths, particularly Little Rock, demonstrate a geological phenomenon known as a balancing rock. There are four distinct types of balancing rocks:

-A glacial erratic is a boulder or large rock that was transported by the movement of glaciers to a resting place on soil, bedrock or on other boulders. These transported erratics usually have different physical characteristics than the surrounding outcrop.

-A perched rock is a large, detached rock fragment that most commonly was transported and deposited by a glacier to a resting place on glacial till (unsorted sediments), usually on a slope or hill. Perched rocks can also be deposited from landslides or avalanches.

-An erosional remnant is a rock formation that remains after large-scale water, wind or other type of erosion. An erosional remnant can sometimes be confused with a glacial erratic, but erosional remnants are made of the exact same type of rock as that that is beneath it.

-A pedestal rock is not a true balancing rock at all but is a continuous piece of rock that has a tiny base that attaches the large boulder to the bedrock. These can be called balancing rocks because it appears to be a separate piece of stone. The undercut base can be attributed to wind or chemical erosion.

In order to log your find, please message me the answers to the following questions:

Please proceed to the Little Rock (waypoint provided on the cache page; also the posted coordinates). If you come around sunset, you may be treated to a spectacular view nearby.

What physical observations can you make about Little Rock? Focus on its color, texture, and size of cracks.
Based on these observations, what type of balancing rock can the Little Rock be categorized as? Explain your reasoning.

Next, proceed to the Big Rock (waypoint provided on the cache page).

What type of surface is the Big Rock balancing on?
Based on these observations, what type of balancing rock is Big Rock?

5. Post a picture with yourself and either Monolith in the background. Your face does NOT have to be present, in accordance with geocaching rules. Instead, you may hold your GPSr or give a thumb’s up to prove you actually visited.