ABSTRACT Recent mapping in southwestern Michigan conducted through U.S. Geological Survey STATEMAP, EDMAP, and Great Lakes Geologic Mapping Coalition projects has produced new interpretations of the origin of the landforms and sediments of the Lake Michigan and Saginaw lobes of the Laurentide Ice Sheet and the dynamics of these lobes. The Lake Michigan lobe advanced southeastward into a proglacial lake at least as far east as the Kalamazoo moraine. During its advance, the lobe extensively deformed the lacustrine sediments it overrode. These structures will be discussed in several pits. When ice backed away from the Kalamazoo moraine, it formed a series of proglacial lakes, several of which were described for the first time in the studies upon which this guidebook is based. As the ice retreated, lowland areas between morainal uplands were utilized by meltwater drainage events, some of them probably catastrophic in nature. The Saginaw lobe stagnated over a broad marginal area as it retreated northeastward toward Saginaw Bay. The resulting stagnant marginal zone is coincident with the subcrop of the Marshall Sandstone. Enhanced basal drainage into the underlying sandstone may have played a role in the dynamics of the lobe. High-relief, supraglacial landforms such as hummocky topography and ice-walled lake plains overprint subglacial landforms in this region, which include large tunnel valleys with inset eskers. Better understanding of the glacial geology of this region is critical to economic development, management of water resources, and exploration for aggregates and other resources.

Ice sheets play a fundamental role within Earth's climate system and in shaping landscapes. Despite extensive research, the maximum extent and basal dynamics of the Laurentide Ice Sheet (LIS) during the last glacial cycle remain elusive and debated in many areas. Recently, cosmogenic nuclides (e.g., 36 Cl, 26 Al, 10 Be) have played an important role in improving our understanding of LIS extent and behavior. Applications of cosmogenic nuclides to LIS research include surface exposure dating of glacial features, constraining magnitudes of glacial erosion, addressing long-term subaerial exposure and ice sheet burial histories, and burial dating of glacial sediments. These techniques have contributed to the depiction of a more extensive LIS than previously reconstructed for the Last Glacial Maximum. In addition, cosmogenic nuclide research has definitively shown that the LIS covered intensely weathered terrain along its deeply dissected eastern margin, where there were steep gradients in the effectiveness of basal erosion related to basal thermal regime. Cosmogenic nuclide applications, those already employed as well as those yet to be discovered, will undoubtedly continue to contribute to our ever-improving understanding of ice sheet history and dynamics.