A landscape perspective

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This article first appeared in INHF's Winter 2006 magazine.

Whitewater Canyon offers clues to bedrock and glacial features that affect landscapes elsewhere in the state.

For example, the Silurian-age dolomite that distinguishes Whitewater Canyon is seen again in the continuous, usually forested, line of bluffs known as “the Silurian Escarpment” (see map above). This prominent terrain feature can be traced diagonally across northeastern Iowa from central Fayette County to southeast Jackson County, where even the course of the Mississippi River is deflected eastward by the resistant dolomite outcrops.

The Silurian Escarpment also marks the boundary between two of the state’s major landform regions. While Whitewater Canyon actually lies within the Iowan Surface region, it is in a transitional area where bedrock exerts more local control on the landscape, as is characteristic of the Paleozoic Plateau region.

Glaciers also produced large-scale landscape changes throughout the state—with ripple effects in Whitewater Canyon.

Massive ice sheets last covered this part of Iowa about 500,000 years ago, leaving behind deposits of pebbly clay, of which only thin, uneroded remnants remain in the well-drained Whitewater Canyon area. This was followed by deposition of wind-blown silt (loess) and fine sand, from roughly 30,000 to 14,000 years ago, which contributed to the thin topsoil on the canyon’s uplands.

Near the end of this period, roughly 21,000 to 16,000 years ago, Iowa and the upper Midwest were plunged into extreme glacial cold. Large areas of permafrost developed in Iowa’s ice-free, tundra-covered landscapes, causing accelerated erosion. Frost action shattered exposed bedrock—including the walls of Whitewater Canyon, leaving slopes of rock rubble still found at its base.

As climates moderated, one last push of glacial ice surged into north-central Iowa between 15,000 and 12,000 years ago. Melting ice revealed the relatively flat, poorly drained landscape that characterizes the Des Moines Lobe region—a sharp contrast to the exposed bedrock and dramatic landscape of Whitewater Canyon. Together they illustrate the remarkable diversity of Iowa’s landscapes.

Visit the Whitewater home page to learn more about this project and ways you can help.

For a more indepth look at the geology of Whitewater Canyon read the accompanying article.

For more information, e-mail the Dubuque County Conservation Board, or call them at (563) 556-6745.