Chazy Fossil Reef, National Natural Landmark and protected area on Lake Champlain islands in New York and Vermont, US

Chazy Fossil Reef is an exposed Ordovician reef, roughly 450 to 480 million years old, within the larger Chazy Formation that runs from Quebec to Tennessee. The National Natural Landmark covers 1,567 acres on three Lake Champlain islands: Valcour and Garden islands in New York, and Isle La Motte in Vermont, where the Fisk Quarry and Goodsell Ridge preserves lie. Its tilted sedimentary layers expose successive strata, so the oldest fossils appear at Isle La Motte's southern end and newer ones toward the north.

The reef is an exposed portion of the Chazy Formation, which runs from Quebec to Tennessee, and its fossils date to roughly 450 to 480 million years ago. The tilted sedimentary layers let visitors see strata from successive periods, with the oldest fossils at the southern end of Isle La Motte and progressively newer layers toward the north. The 1,567-acre landmark was dedicated as a National Natural Landmark in May 2009.

The name comes from the Chazy Formation, a rock unit named after the town of Chazy in Clinton County, New York. On Isle La Motte the Fisk Quarry Preserve holds the old quarry where stone was cut, while Goodsell Ridge Preserve protects fossil-bearing ledges. Both are managed by the Isle La Motte Preservation Trust and open to the public.

The protected reserves are open to visitors with walking paths through the limestone formations and fossil exposures. Wearing sturdy footwear is recommended as the terrain can be uneven and exposed to weather conditions.

The reef spans three Lake Champlain islands: Valcour and Garden in New York, and Isle La Motte in Vermont, where the Fisk Quarry and Goodsell Ridge preserves are open to the public. On Isle La Motte the oldest fossils lie at the southern end, with progressively newer layers toward the north.