Monadnock Trails

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About Monadnock

Monadnock Vegetation

Old Trail Descriptions

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Tags: Monadnock, Monadnock Geology, New Hampshire Hiking, New Hampshire Maps, Mount Monadnock, Jaffrey, NH, Hiking New Hampshire

Monadnock Geology

Below: Monadnock looking south

Monadnock Geology

Grand Monadnock is a striking geological feature known as a monadnock; an isolated mountain composed of resistant rock surrounded by a peneplain.  A monadnock is a remnant of higher mountains.  Mount Monadnock at 3165 feet stands 2000 feet above the southwestern New Hampshire hill country and has a commanding view over central New England.  About 200 million years ago the mountains of New England may have been as high as the Himalayas.  Over the millions of years, mountains have risen up and been cut down to their modest present day heights.  Because of the erosion New England is roots to a much higher land.  Most of the mountains have eroded away.  There are areas of more resistant rock which left monadnocks, mountains that abruptly rise over rolling hills and are isolated.  Named after the most famous, Mt. Monadnock, monadnocks have very old origin.

Mount Monadnock is primarily comprised of metamorphic rock, which about 400 million years ago was laid down as sediment under a sea. The sedimentary rock was cooked and compressed under mountains that pushed skyward like today's Himalayas when the Americas collided with Europe and Africa.  The rock consisting of mainly what is called Schists and Quartzites has been metamorphosed destroying any fossils in the rocks.  The "ancient bird tracks" you may see on the mountain are a result of the rock being cooked and compressed.  There was a lead mine southeast of Bald Rock.  There are Granite intrusions in the rock which was molten magma that hardened into rock under the surface of the earth.  Not much of value is in the rock that is speckled with red garnets with occasional veins of white quartz on Monadnock.  The land eroded over the eons leaving Monadnock an isolated mountain surrounded by a rolling hilly elevated plain called a peneplain.  The plain has been lifting since the last ice age and New England's hilly terrain is actually even-topped hills cut by streams and rivers and appears flat from a distance if you look south to the horizon from the summit of Monadnock.  Looking southwest the Berkshires appear like a plateau and are remnants of a higher land as well.

Below: Billing's Fold near summit;
Fold is evidence that Monadnock is a remnant of much higher mountains.

Glaciers also have left an imprint on Monadnock and the surrounding landscape.  Glaciers have shaped Monadnock and there is evidence of glaciers covering Monadnock from giant boulders left by glaciers such as the Sarcophagus which looks like a large stone crypt along the Pumpelly Trail.  The last time span that glaciers raked over the entire landscape was known as the Pleistocene epoch which began 2.5 million years ago and departed a short 15,000 years ago.   In the picture below on Bald Rock and you can see glacial scratches, known as glacial striations, where rocks carried by the glacier scraped the ledge on Monadnock.  The glaciers also plucked rock from the southeastern slopes of New England making those slopes steep.  Glaciers which created dramatic U-shaped notches in the White Mountains to the north also made Monadnock's western and eastern slopes steep, such as on the White Dot Trail on the east side, or the Marlboro Trail on the western side of the mountain.  The north slopes tend to be more gradual as the glacier rode over the mountain such as along the Dublin Trail to the summit but cliffs drops steeply down just south of the summit as the glaciers plucked rock away along joints in the bedrock.  The glaciers also left a number of ponds surrounding Monadnock resulting from the ice pressing in spots now filled with water.  Numerous natural ponds surrounding Monadnock are usually common in glaciated lowlands such as the lakes region of New Hampshire as well as in Quebec, Canada.  Geology can actually be very interesting when exploring Monadnock.

Below Left: Glacial scratches
Below Right: Shade highlights steep southeastern slope

Researched and Composed By Frederick Pitcher, 2010 Edition (see contact author)
References :
Guide to New England Landscape©1977 (Globe Pequot) Neil Jorgensen
Geology of the Monadnock Quadrangle©1949 (NH Planning and Development Commission) Katherine Fowler-Billings
Monadnock Guide©1970 (SPNHF) Henry I. Baldwin
The Forging of Our Continent©1968 (American Heritage Publishing Co.) Charlton Ogburn Jr.
Planet Earth: Ice Ages©1983 (Time/Life Books) Winsdor Chortlon

Tags: Monadnock, Monadnock Geology, New Hampshire Hiking, New Hampshire Maps, Mount Monadnock, Jaffrey, NH, Hiking New Hampshire

Jaffrey Weather Forecast, NH

The weather above is for the base of the mountain.