Page 5 - DesMoinesRiver

THE NATURAL HISTORY OF THE DES MOINES RIVER

The Des Moines River rises at the Shetek Lake 1840 GLOUpper: map showing the maximum extent of the Des Moines Lobe during the last glacial
Group in Minnesota and flows 525 miles passing di- advance in Iowa. Lower: 1849 GLO map of the Des Moines River superimposed on a LiDAR
agonally through Iowa and joining the Mississippi at topographic image.
Keokuk. Although perhaps following the course of
an earlier “proto-Des Moines” channel, the present Map of Des Moines River
valley originated about 12,300 years ago as a major
conduit for glacial meltwater (Bettis and Hoyer The University of Iowa Off ice of the State Archaeologist
1986). The large quantity of water flowing away from
the melting continental glacier carved a deep, often
gorge-like, channel into the underlying Wisconsinan
loess, the older glacial tills, and the Pennsylvanian bed-
rock. The Des Moines River also cross-cut the Beaver
Creek channel north of the city of Des Moines, captur-
ing that older river’s drainage (Bettis and Hoyer 1986).
By 11,500 B.P. (Before Present), the last glacial ice, the
Des Moines Lobe, had left the state and the flow of water
was reduced to the smaller volumes seen today (Bettis et
al. 1996:2; Artz 2013).

The original General Land Office (GLO) surveys of south-
eastern Iowa offer clues as to what the early modern plant
communities along the river might have been like. By the time
the GLO surveys were conducted in the 1840s, large tracts of
the Des Moines River valley and adjacent uplands were already
under cultivation. Uncultivated portions were largely covered
with forests or more open woodlands, with a few tall grass
prairies on upland divides. Information in the GLO survey notes
(Iowa Land Office 1938) indicates that three kinds of forests
were present. The Des Moines River floodplain was charac-
terized by water loving trees such as sycamore, cottonwood,
maple, and hackberry. The loess-mantled uplands and benches
supported oak-hickory or scrubby oak-hickory-hazelnut com-
munities. Data from soil analyses indicate that these plant
communities were widespread before the land was cleared for
cultivation (Artz 1991:7–8).

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