[1] The oldest existing shorelines were formed after retreat from the Greatlakean advance (previously called the Valders), sometime around 11,000 years B.P.

Lake Duluth overflowed south through outlets in Minnesota and Wisconsin at an elevation of around 331 m above sea level.

In the early part of the recession of the ice front Lake Duluth, with an outlet from the Brule River Valley through the St. Croix River Valley, was present in the western part of the Lake Superior Basin.

It stood in the part of the St. Louis River drainage basin northwest of the border of the Superior lobe.

Several narrow bays of Lake Duluth, extended up each of the tributaries of Ontonagon River south of the copper range.

[3] The eastern limits of Lake Duluth on the south shore have been found to be at the Huron Mountains, in Marquette County, Michigan.

It is known, however, that the lake extended at least to the Kaministiquia River basin west of Fort William, Ontario.

It is probable that there was a protrusion of the ice into Keweenaw Bay at the time of greatest expansion of Lake Duluth, and the east end of the Keweenaw Peninsula may have been beneath the ice down to the time the Lake Duluth waters were drained eastward.