Much of the area is mantled by till, whose thickness exceeds 100 feet in places. A complex history of glacierization is recorded by drumlins of diverse patterns, by eskers, and by features eroded in bedrock. The eskers form a dendritic pattern across the area, and are believed the result of regressive deposition from consequent superglacial streams. Some transitory proglacial lakes existed, but there has been no post-Wisconsin marine submergence of the area.
The recorded sequence of ice movements through the area from oldest to youngest is (1) to southeast, (2) to north, (3) to N. 30 W., and (4) to N. 60 W.
A carbon-14 age determination of 4140 150 years was made on peat buried by the last ice advance.