The Bull Lake glaciation is the name of a glacial period in North America that is part of the Quaternary Ice Age.
[3] It draws its name from Bull Lake in Wyoming in the United States, where well-preserved moraines from this glacial period were first described.
Although Blackwelder originally believed the Bull Lake glaciation occurred during the early Wisconsin Glaciation (the last major advance of glaciers in the North America), new data generated and described by geologist Gerald M. Richmond in the 1940s and 1960s more accurately dated the glacial period to the Illinoian Stage.
It did not cover the entire North American continent but rather just the eastern slopes of the southern Rocky Mountains.
Generally speaking, it extended from northwestern Montana south to the San Juan Mountains in Colorado.