Nature Notes: The Champlain Thrust Fault at Rock Point – A Geologic Wonder

Nature Notes is a column provided by our partner, The Lake Champlain Land Trust, regarding natural and ecological landscape at Rock Point.

Geologists from around the world travel to Rock Point to marvel at its geologic features.

The Natural Area is home to one of the most visible and dramatic exposures of a thrust fault in Eastern North America. And now, with the Natural Area’s trail restoration project complete, geologists and hikers can easily access and study Rock Point’s geologic wonders.

The main geologic attraction at Rock Point is the Champlain Thrust Fault. This world-renowned thrust fault exposure consists of two types of bedrock—the sand-colored Dunham Dolomite on top and the dark grey Iberville Shale below. Geologists estimate that the bottom layer (Shale) was formed around 460 million years ago during the Ordovician Period, while the top layer (Dolomite) was formed earlier—between 500 and 540 million years ago during the Cambrian Period.

This inversion of layers, with the older rock formation on top, was caused by an ancient mountain building event known as the Taconic Orogeny. During this time, tectonic forces pushed the landmasses currently underlying New Hampshire and Maine into present-day Vermont, creating the Green Mountains. High pressures cracked and buckled the bedrock during this violent event, thrusting the older Dunham Dolomite up and over the Iberville Shale layer.

In addition to this uncommon layering, the Champlain Thrust Fault at Rock Point is unique in that it is exposed at eye-level. Thrust faults exist around the world, but many are buried underground or are found in inaccessible regions. Rock Point provides a rare, up-close and accessible view of this unique geologic phenomenon. To visit the thrust fault, take the appropriately-named Thrust Fault Trail or the Sunset Ridge Trail, and walk down the stone staircase to the shoreline (this access location is marked on the official Rock Point Trail Map).

The Lake Champlain Land Trust is the conservation partner of the Rock Point Sanctuary. The Land Trust holds the conservation easements permanently protecting the natural, scenic and recreational resources of the Rock Point land. The Lake Champlain Land Trust is a member-supported, non-profit organization working with you and your community since 1978 to save land, conserve places to hike and paddle, and protect Lake Champlain's water quality. For more information and local places to explore nature, visit our website (www.lclt.org).