Ignore the famed waterfalls and focus on Goat Island cliff in the middle. That wall is the Niagara Escarpment, caused by relatively hard rocks at the top holding the land underneath together, until it erodes away from the side. This two level land break—all erosion and not earthquake fault—is the key geologic feature to understanding the Great Lakes.

Much of the escarpment is in Canada, and even where it crosses the border to form Niagara Falls, it’s easier to see from the Canadian side as above. It runs along the south shore of Lake Ontario, across Niagara Falls (above) where it sets the level of Lake Erie, northwest through Ontario where it guides the Bruce Trail, up along the north shore of Lake Huron where it splits off Georgian Bay and shapes Lakes Huron and Michigan, along Michigan’s Upper Peninsula where it separates Lake Superior, and down the Door Peninsula past Green Bay in Wisconsin. After driving around the Great Lakes, it’s apparent how the water levels depend on the escarpment: Superior is the highest above both ends, Michigan and Huron are the same level in the middle, and shallow Erie is a little lower, held back at Niagara Falls, before that river drains into the lowest lake, Ontario.

UNESCO defines the Biosphere as the mostly forested area of Ontario between Niagara Falls and Tobermory on the tip of the Bruce Peninsula next to Georgian Bay, roughly 500 miles along the escarpment. The geologically interesting landscape holds great biodiversity in wetlands, coastline, deciduous & conifer forests, and rocky bluffs, perhaps the most in Canada. And there are many opportunities to explore, photograph wildlife, hike, drive or boat nearby. I hiked on the Cup & Saucer Trail on Manitoulin Island, the world’s largest freshwater island, when traveling around the Great Lakes. There, the escarpment is eroded on both sides, providing many views along its edge, including Lake Manitou below.