SURFICIAL GEOLOGY OF CASS COUNTY, MICHIGAN

Cass County contains complex glacial landforms and sediments that formed during advance and retreat of the Lake Michigan and Saginaw Lobes of the Laurentide Ice Sheet during the last glaciation. The Lake Michigan Lobe (LML) advanced from the NW and the Saginaw Lobe (SL) advanced from the NE into the county resulting in complex and often overlapping interlobate deposits in the eastern portion of the county.

The prominent uplands of the SW-NE trending LML-Kalamazoo Morainic complex and associated large southeast sloping outwash fans dominate the western half of the county. It consists of two main ridges, the Outer Kalamazoo Moraine to the east and the Inner Kalamazoo Moraine to the west, both of which broadly climb in elevation to the NE. In places there is a third ridge between them. The location and orientation several tunnel valleys also provide evidence that both the LML and SL occupied Cass County different times.

Glacial Lake Dowagiac which was a major glacial lake and glacial meltwater sluiceway at about 19,000 years ago running NE to SW the between the Valparaiso ice to the NW and the Inner Kalamazoo Moraine to the SE. It cut several streamlined residual ridges, a terrace above the floor of the valley and a linear escarpment on the east side of the Inner Kalamazoo moraine all providing evidence for the large volumes of water that flowed through the valley as a result of the catastrophic overflow of proglacial Lake Dowagiac as part of the Kankakee Torrent.

Other glacial features within the county include eskers, parallel thrust ridges, streamlined features, meltwater channels and glacial drainageways and numerous ice-walled lake plains on the morainal uplands. A large sand sheet and dune field as well as many isolated inland dunes occur mostly in the NW part of the county associated with Dowagiac River valley.

The bedrock topography, bedrock valleys and drift thickness, and were mapped using the HVSR passive seismic method. As series of NW trending buried bedrock valleys occurs in the north half of the county and are extensions of deep bedrock valleys that run NW across Van Buren County to the north. Glacial deposits average 310 feet thick and range in thickness from 115 to 717 feet which is the thickest known in the southern half of the Lower Peninsula of Michigan! A previously unknown gravel aquifer was discovered in one of the bedrock valleys.