Visitor's Guide To Franklin County Geology

by Richard D. Little

Franklin County,  Massachusetts: the world’s best place to study geology! Be prepared to be amazed! Most people think of geology as “just a bunch of rocks”, but exciting Earth events are recorded in rocks and landscapes, too. Franklin County has magnificent landscape scenery: mountains, waterfalls, rushing rivers and meandering ones, such as New England’s longest river, the Connecticut. We also have quite a bunch of rocks, too, including famous ones with dinosaur footprints plus we also have something truly unique: the world’s only petrified armored mud balls. Intrigued?

More on those later.

Here is the geology story of Franklin County and surroundings, greatly summarized. In the Paleozoic Era western Franklin County was the underwater edge of the North American continent. Tectonic plates came from afar and collided to make the super continent of Pangea. Those collisions created metamorphic rock out of the old ocean sediment. Franklin County was now “landlocked” in the middle of mountains, the young Appalachians now mostly eroded. The photo is the prominent roadcut along Rte. 2 in Erving. It shows metamorphic rock (schist) with quartz “pods” called boudins (French for “sausage”). These are rocks from the deep middle of mountains exposed by three hundred million years of erosion.

Basalt Columns, Highland Park, Greenfield. Photo Credit: Franklin County Chamber Library
Block Diagram Illustrator: Will Sillin

In the Mesozoic Era Pangea split and a long faulted “rift valley” shaped Franklin County, which looked much like the stark, dramatic landscape of Death Valley. Streams washed great volumes of gravel, sand, and mud into this valley. Sometimes mud balls rolled down streams and became armored with pebbles. Dinosaurs left footprints. Also, lava erupted along faults and “fissure flows” of basalt flooded across the valley, ponding over 100 feet thick. More sedimentary layers covered the lava and continued fault movements (earthquakes) tilted the whole “sandwich” of sedimentary layers with a lava middle.

Skipping about 200 million years ahead to the late Cenozoic Era, glaciers advanced and melted. The last glacier had a prominent glacial lake that followed the melting ice front from central Connecticut and through Massachusetts and northward. This was glacial Lake Hitchcock which finally drained about 14,000 years ago. Lake Hitchcock’s deposits are a major shaping force of today’s landscape along the Connecticut River Valley.

The lake’s thick accumulation of sediment caused area rivers to do strange things. The Deerfield and Millers Rivers both turn north, opposite the regional land slope, and enter the Connecticut facing upstream. The Connecticut also suddenly and uncharacteristically, abruptly bends to the west near the French King Bridge. There are deep river holes here (old waterfall plunge pools). You need to take a summer scenic boat trip with a depth finder to appreciate this hidden history.

At Shelburne Falls an effect of Lake Hitchcock caused the Deerfield River to carve the famous “Glacial” Potholes exposing some of the most beautiful rock in the world, a metamorphic type called gneiss (“nice”). Strange stories, “nice” indeed!


All these scenic wonders can be experienced from roadway viewing spots and / or short walks, and they are all 30 minutes or less from Greenfield. Everything is scenic, interesting, sometimes unique (like the armored mud balls), easy to access, and close-by.

Many visitors and locals travel along Rte. 2, the Mohawk Trail. This east-west road cuts across the middle of Franklin County as well as across the geologic rock trends. You get to see rocks and landscapes beautifully displayed. All three rock types can be easily seen: metamorphic, igneous, and sedimentary, plus there is a notable variety and diversity of landscapes from mountainous canyons and waterfalls to meandering streams to explore. Fishing, hiking, camping, skiing, white-water rafting, boating and lots of nature viewing are all options.

Whether you are a visitor or a resident, I have selected a few spectacular places to start your explorations. Exact directions and information are found in the new “Exploring Franklin County” book or you can “Google” for directions.

A “START HERE” DESTINATION: Greenfield Community College Geology Path (by parking lot F). There is a Guide in the metal box. Rare armored mud ball specimens are on display. See below for armored mud ball origins.

GREAT VIEWPOINTS: Poet’s Seat, Greenfield; Mt. Sugarloaf, South Deerfield; High Ledges, Shelburne Falls

WATERFALLS: Listed according to height. Tannery Falls, Savoy; Turners Falls, Barton Cove (abandoned falls), Gill; Chapel Falls, Ashfield; Roaring Brook, Sunderland.

FOSSILS: Beneski Museum at Amherst College….not in Franklin County, but “world class”; Barton Cove’s historic footprint quarry, Gill; Note: insects and other invertebrates left lots of tracks, trails, and burrows in our Jurassic sedimentary rocks. While these are not spectacular like a reptile print, they are fossils and these pits, bumps, and scratches are commonly seen along the Mesozoic red rock bedding planes. Also, search riverbank rocks below the Turners Falls Dam.
LAVA: Highland Park, Greenfield; Rte. 2 Factory Hollow, Greenfield.

UNUSUAL AND DRAMATIC ROCK OUTCROPS: GCC Geology Path; Erving, Rte. 2; Brush Mt., Northfield; Shelburne Falls Potholes; Marble Natural Bridge, N. Adams; Highland Park’s Sachems Run Trail, Greenfield.

CAVES: Catamount, Colrain; Mt. Toby, Sunderland

GLACIAL FEATURES: Drumlins (Gill, drive through them along Turners Falls Rd.); Esker, Old Vernon Rd, off Rte. 142, Northfield; Glacial striations and roche moutonnee, Brush Mt., Northfield; Kettle Ponds: Green Pond & Lake Pleasant, Montague; Cranberry Pond, Sunderland.

RIVER TERRACES: Deerfield Main St.; W. Northfield rte. 142 – Caldwell Rd.

LAKE HITCHCOCK FEATURES: Sunderland Delta (“Delta Gravel Co.”) Rte. 116, Sunderland; Rte. 142, W. Northfield, delta and lake bottom deposits

RIVER TRIP: SEASONAL -- Heritage River Boat Cruise from Northfield to Barton Cove and return. Sponsored by First Light Power Company. Seasonal. Check online for contact information.

While not in Franklin County, these are close and very special:

Amherst College’s Beneski Museum of Natural History.

Trustees of Reservations Dinosaur Footprint Site by the Connecticut Riverbank along Rte. 5 in Holyoke.

Skinner State Park and Mt. Tom State Reservation. These locations along the Holyoke Range (basalt) offer great views and interesting rocks, too.


Armored mud balls are very rare, only being noted from about ten locations world-wide and those are mostly from very rural, mountainous locations. Franklin County specimens, when they are encountered, are sometimes found in locally quarried rocks. This means that they have been removed from their bedrock “home” and can be handled if small enough or transported and displayed.

The armored mud balls beautifully seen in the photo are in a piece of quarried sandstone, part of a historic bridge foundation (now dismantled) between Turners Falls and Gill. This rock is now preserved in the GCC Geology Path collection. Ruler is 6 inches for scale.

Armored mud balls form when hard clay falls into a stream, tumbles downstream and becomes round and soft and sticky on the outside. Pebbles stick to the rim. This is the armor. Then these fragile forms have to be quickly buried and eventually turned to stone. These Connecticut Valley sedimentary events were happening in the Jurassic Period about 200 million years ago.

Lithified (turned to stone) armored mud balls are not only very rare, but the ones in Franklin County are the only ones that can be sampled….held in your hand or displayed in a museum. This is because they are in quarried blocks. All other armored mud ball examples are in mountain or cliff outcrops and are not able to be removed. Therefore, every specimen of lithified armored mud balls you will see in schools and museums is from Franklin County. They are not only fun and intriguing to see, they are truly unique. I think this, by itself, is reason to immediately drive to Franklin County for a few days of exploring!

Franklin County is a very special place. It is quite different from other areas of New England. With lava flows and abundant red sedimentary rock, the same type as Ayers Rock (Uluru) in Australia, as well as beautiful metamorphic deep-Earth rock, Franklin County is a geologic adventure in rocks and landscapes that all can learn from and enjoy. This is the best place in the world to study geology!

Do you wish to learn more about Franklin County’s geology and where to see it? A new 200 page guide, “Exploring Franklin County” is now available via bookstores or mail order. Please see below the details.

Richard D. Little, 2020, Exploring Franklin County, ( 2nd revised and expanded edition), 200 pages, spiral bound, Earth View LLC, Easthampton MA. Available at local bookstores and this web site that also has more geology You may also contact Prof. Richard Little at with questions, comments, or to get on his "local geology" email list.

Richard Little has BA and MA degrees from Clark University and the University of Southern California, respectively. In 1969 he was fortunate to be hired by Greenfield Community College and discover the Connecticut River Valley area. He has written two books and produced two DVDs about Connecticut Valley geology. From teaching and local exploring, he concluded that this is the best place in the world to study geology. Explore Franklin County and let him know what you think.

After many years living in Greenfield on the muddy floor of old Lake Hitchcock, he moved up to the shoreline in Easthampton, MA, on the side of a drumlin. He sometimes thinks about sitting on a stranded iceberg in his backyard if he was here during summer 16,000 years ago.

More Outdoor Recreation Opportunities

Event Information

July 17

Great Hall Exhibit: Remnants

July 17

Shelburne Falls Military Band Concerts

July 18

Great Hall Exhibit: Remnants

July 18

POINT 5K A Summer Eat & Run

July 18

Coop Concert

July 18

Live Music on the Patio

July 19

Great Hall Exhibit: Remnants

July 19

Kidleidoscope Story Hour: Snakes