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Connecticut Geology

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esker and kettles

Eskers and kettle ponds like these in Manitoba lurk in Connecticut.

Natural Resources Canada

I got a note from a Los Angeles reader who was visiting Connecticut. The countryside excites him! Now I was raised in that region, and when I moved to California the countryside there excited me. We're always used to the land where we grew up, and it takes a fresh eye to remind us of its charms. The landscape and geology of Los Angeles is a topic in itself, but let's look at Connecticut. It happens that the two areas are about the same size, but they differ in almost every respect.

Connecticut is missing most of the real geologic spectacles of the American East: the barrier beaches from Cape Cod to the Carolinas, the high granite balds of New Hampshire and Maine, the noble Palisades facing Manhattan, the Delaware Water Gap, the caverns of Kentucky, New York's Finger Lakes, the keys and sinkholes of Florida, the sweeping valley-and-ridge country of the central Appalachians, the Fall Line and Piedmont, the Great Lakes. But rocks of many ages and types crop out in Connecticut, evidence of a long and eventful history.

Connecticut's Geologic Youth

Connecticut had an active youth with lots of landmasses colliding and breaking apart, mountain ranges rising and being eroded, their sediments washing into nearby marine basins. It has been part of several different ancient landmasses: Rodinia, Pangea, Laurasia, Avalonia. The continent ripped open there during the Late Proterozoic era 700 million years ago, giving birth to an ocean named Iapetus. Then Iapetus's edges came together again squeezing the sea out of existence.

All that activity left the rocks cooked and kneaded—metamorphosed. What it means for Connecticut rockhounds is that many of the oldest rocks in the state are excellent mineral collecting localities.

Later, another ocean was born there, the initial stretch marks in the continental crust filling with lava flows where New Haven and Hartford sit today. Dinosaurs left footprints there, some of which are preserved in Dinosaur State Park. That young ocean widened into the Atlantic, its far shore becoming northern Africa. For the last 150 million years or so Connecticut has been pretty quiet tectonically, riding along on the edge of North America.

Pleistocene Connecticut

The Connecticut landscape today reflects that quiet period. The mountains raised in the Paleozoic Era (550 to 245 million years ago) eroded down to gentle plains during the following Mesozoic and Cenozoic Eras. The ocean rose and fell over the course of the ages, too, washing away or rearranging the eroded sediments. These events are recorded in rocks all the way down the Eastern Seaboard from New York Harbor to the Florida coast. Connecticut used to be like that too—until just a few million years ago the region was a deeply weathered land of subdued topography.

Then came the Ice Ages. Great continental glaciers smothered Connecticut, bulldozing its soils away to the south where they left a pile named Long Island. When they melted, the glaciers dropped the sediments they were carrying from farther north. The result is a deposit called till, a mixture of everything from clay to house-sized boulders. And today the streambeds and gardens of Connecticut are full of rock chunks from Massachusetts, New York, Vermont, and Quebec.

Connecticut Today

These days the Constitution State is a green, humid place with summer nights full of fireflies. But underneath the lush and placid countryside is a landscape of glacial features, much like the bare vistas of far northern Canada today. Those who know what to look for can find the kames, the eskers, the drumlins, and the other peculiar landforms of glaciated areas all over Connecticut.

This part of the world is very different from Los Angeles. There are none of L.A.'s rugged skylines—the highest point in the state, at 725 meters, is only a foothill in California terms. It's frustrating if you like long vistas and dramatic rocky slopes. But Connecticut offers privacy, and the intimate charm of water moving over stones in small valleys. It offers an intricate coastline with picturesque stony shores, and seas that favor boaters over surfers. And there are rock types and minerals that can't be found anywhere near Hollywood.

PS: Angelenos will find a glimpse of home in Connecticut—a lovely scene of the Triassic Period, 200 million years ago, when mountains just like the San Gabriels rose east of New Haven. It's a mural at Dinosaur State Park. Also, the state feels the occasional earthquake.

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