36. BEDROCK IN VICINITY

Banded boulder near Peabody River's Flat Rock Pool

It is perhaps something of a stretch to include the topic of bedrock and geology in this Campground history. Then again it is quite an historical topic and many campers enjoy this sideline. How about we just call it the area's "very early" history!

In approaching this topic we owe much to a 1975 government report entitled Geology of the Gorham Quadrangle by Marland Billings and Katherine Fowler-Billings. Below are some relevant excerpts from that classic research piece:

SOUTH OF GORHAM, Page 74: One-half mile south of Gorham, diorite is exposed for 150 feet along the Peabody River. It is bounded both to the north and south by Concord Quartz Monzonite, Figure 49 below, at altitude 830 feet on the Peabody River.



Figure 49: Important bedrock example
at altitude 830 feet on the Peabody River.

SOUTH OF GORHAM, Page 82: patterns of post-metamorphism dikes, Figure 51e below, intersecting dikes; width of dikes exaggerated for clarity; 14" dike is metadiabase, 6" dike is "mafic rock", at altitude 910 feet on the Peabody River.

Figure 51e: Important bedrock example
at altitude 910 feet on the Peabody River.

PINE MOUNTAIN, Page 18: Interbedded feldspathic quartzite and spangled mica schist is found throughout the the Littleton formation, but is especially important on Pine Mountain... Good examples may be seen on Pine Mountain one quarter mile south of the fire tower where beds dip 80 degrees NW with the top to the northwest.

PINE MOUNTAIN, Page 68, The contact of the concord Quartz Monzonite with the Littleton formation is superbly exposed on the south slopes of Pine Mountain for a length of over 2000 feet (Pl. 2)... Plate 2 shows that the contact, despite its very irregular trace, maintains a rather uniform altitude between 1900 and 2150 feet. The contact is everywhere knife sharp.

PINE MOUNTAIN. Page 70, Map b below. Irregular bodies intruding interbedded mica schist and feldspathic quartzite of Littleton Formation. b. Pine Mountain, altitude of 2270 feet southeast of summit.

Map b: Important bedrock example at
altitude 2270 feet on Pine Mountain.

SOUTH OF DOLLY COPP, Page 17: A thin bed of quartz conglomerate extends northward from a point one quarter mile east of Emerald Pool to one mile south of Dolly Copp Campground, a total distance of three miles.

The best exposures are at an altitude of 1650 feet on the ridge extending up to peak 2587 (2584) southwest of Dolly Copp Campground and at an altitude of 1520 feet on the West Branch of the Peabody River.

SOUTH OF DOLLY COPP, Page 18: The shiny fine grained mica schists are especially well developed in a band one and one half to two miles wide west of the Peabody River; they extend southwest from Dolly Copp Campground to the Mount Washington Auto Road.

Fresh surfaces are gray, but weathered surfaces are brown due to limonitization of pyrite. The essential minerals are muscovite, biotite, and quartz. The schistosity, which parallels the bedding, displays a well defined lineation...

NINETEEN MILE BROOK, Page 64: Diorite is exposed for one-half mile along Nineteen Mile Brook between altitudes of 1560 and 1780 feet. On the map it is shown as two separate bodies, due to the exposure of a small mass of two-mica gneiss at an altitude of 1710 feet.

EMERALD POOL, Page 21: The lime-silicate rocks are very distinctive, offering a welcome relief from the extensive schists, feldspathic quartzites, and paragneisses that constitute most of the Littleton Formation. the most southwesterly exposure in the Gorham Quadrangle is at Emerald Pool on the Peabody River, where the member is 27 feet thick.

OVERALL COMMENT, Page 92: Since the Jurassic the area has been undergoing stream erosion. The present topographic features began to develop a few million years ago. The details of the topography were profoundly modified during the Pleistocene by glacial erosion and deposition.

MAP XXXXXXXX The coloration of the rocks and boulders along the Peabody is very attractive. According to the 1975 “Geology of the Gorham Quadrangle” by the NH Department of Resources and Economic Development, Dolly Copp Campground is underlain by bedrock known as Concord Quartz Monzonite, “a very common rock in New Hampshire.”

This is described as medium grained, light gray composed of potash, feldspar (whitish or pink), oligoclase, quartz (translucent white or gray), biotite and muscovite (white or silvery mica flakes). Its age is given as New Hampshire Plutonic Series, Middle Devonian of the Paleozoic (something like 390 million years old).

But just about at the south end of the Campground, at the historic bridge crossing, the same source map indicates that the bedrock type changes to Littleton Formation interbedded mica schist and micaceous quartzite. This rock is a little older, from the Early Devonian period. The bedrocks can best be seen at Flat Rock Pool, Rangers Pool or on Culhane Brook upstream from the bridge.