The Niagara Escarpment is a long escarpment, or cuesta, in the United States and Canada that runs westward from New York State, through Ontario, Michigan, Wisconsin and Illinois. It is composed of the Lockport geological formation of Silurian age, and is similar to the Onondaga geological formation, which runs parallel to it and just to the south, through the western portion of New York and southern Ontario. The escarpment is most famous as the cliff over which the Niagara River plunges to form Niagara Falls, for which it is named.
The Niagara Escarpment is the most prominent of several escarpments formed in the bedrock of the Great Lakes. It is traceable from its easternmost point in New York State, starting well east of the Genesee River Valley near Rochester, creating one large and two small waterfalls on the Genesee River in that city, thence running westwards to the Niagara River forming a deep gorge north of Niagara Falls, which itself cascades over the escarpment. In Southern Ontario it stretches along the Niagara Peninsula hugging close to the Lake Ontario shore near the cities of St. Catharines and Hamilton and Milton where it takes a sharp turn north toward Georgian Bay. It then follows the Georgian Bay shore northwestwards to form the spine of the Bruce Peninsula, Manitoulin, St. Joseph Island and other islands located in northern Lake Huron where it turns westerwards into the Upper Peninsula of northern Michigan, south of Sault Ste. Marie. It then extends southwards into Wisconsin following the Door Peninsula and then more inland from the western coast of Lake Michigan and Milwaukee ending northwest of Chicago near the Wisconsin-Illinois border.
The dolostone cap was laid down as sediment on the floor of a marine environment. In Michigan, behind the escarpment, the cuesta capstone slopes gently to form a wide basin, the floor of an Ordovician-Silurian tropical sea. There the constant depositing of minute shells and fragments of biologically-generated calcium carbonate, mixed with sediment washing in by erosion of the virtually lifeless landmasses eventually formed a limestone layer. In the Silurian some magnesium substituted for some of the calcium in the carbonates, slowly forming harder sedimentary strata in the same fashion. Worldwide sea levels were at their all-time maximum in the Ordovician; as the sea retreated, erosion inevitably began.
In Southern Ontario, the Bruce Trail runs the length of the escarpment from Queenston (Niagara Peninsula) to Tobermory (Bruce Peninsula). The very busy Highway 401 in Southern Ontario also crosses the Niagara Escarpment, beginning its long descent through rolling hills, farmland, and towns west of Milton.
Hamilton, Ontario is situated on the escarpment in such a way that the north end of the city is below and the south part above. Affectionately referred to as "the mountain" by its residents, the escarpment is both an attraction and a hindrance to everyday life. Bridging the divide are a number of roads or "mountain accesses" that separate the urban core below from the suburban expansion above.
High Cliff State Park in Wisconsin shows how modern and prehistoric humans used the escarpment for not only cultural reasons but economic gains as well. There are a number of different animal and geometric effigy mounds, and the remains of an turn-of-the-century limestone quarry and kiln within the park.
In February 1990, the Niagara Escarpment was designated a World Biosphere Reserve by UNESCO, making it one of 12 in Canada. Development and land use adjacent to the escarpment is regulated and the biosphere protected by the Niagara Escarpment Commission, an agency of the Ontario government.