 During this period of time—known as the Lockhart Phase of Lake Agassiz—water flowed south from the lake into the Mississippi River and into the Gulf of Mexico.In the US, the Pembina Escarpment is a Level 4 ecoregion, as defined by the U.S. Environmental Protection Agency.The ecoregion covers , and is part of the Level 3 Northern Glaciated Plains ecoregion.