Continuing from my 1999 article in "Michigan History":
The next piece of the puzzle of LaSalle's route is the location of the fens and marshes through which they struggled. In the early spring the trees and shrubs were leafless and there was flooding everywhere from melting snows. Since LaSalle's journey occurred before the southern Lower Peninsula was logged, drained and plowed, the water table was much higher than it is today.
A cursory reading of LaSalle's account or the reading of secondary sources leaves the impression that the party waded through one vast swamp (wetland with trees) or marsh (wetland with sedges and rushes). Actually, they faced a series if marshes and swamps interspersed with higher and drier uplands, ridges and knolls.
LaSalle encountered this series of wetlands after crossing the floodplain of the Battle Creek River, probably near Pennfield northeast of Battle Creek. Going east today across the northern tier of townships in Calhoun County there are several tributaries of the Battle Creek River that flow to the north or northwest. At Duck Lake the tributaries of Rice Creek flow south or southwest. Further eastward lies the divide between the Kalamazoo River drainage basin and that of the Grand River. Continuing eastward, there are two northward flowing tributaries of the Grand River and then the Grand its self. Lowlands that must have been flooded swamps or marshes in the spring of 1680 border all these streams.
U.S. Department of Agriculture soil maps aid in determining the extent and nature of some of these wetlands. These maps show in great detail the types of soil and provide data on the slopes of the land and susceptibility to flooding and ponding, plus water table relationships. The key soil type is muck. Where muck exists today, marshes existed earlier. The maps identify and locate other types of soil subject to frequent flooding or with such a high water table that the land is unsuitable for septic tanks and drain fields. Soils that are flood-prone or water saturated today were wet and flooded during the spring high water in the late seventeenth century.
Highlighting the mucks and the flood-prone soils creates a mosaic that represents a birds-eye view of the wetlands and the intervening dry land over which the LaSalle party traversed. The longest stretch of marsh that the men waded through was twelve miles of almost continuous lowland, located today in Calhoun County's Convis, Lee and Clarence Townships. Interstate 69 crosses the west end of this stretch about one and one half miles north of the N Drive North exit.