REARRANGING THE EARTH
The surface of the earth is always changing even without our help. Rocks are being worn away and moved by water, topsoil is being rearranged, rivers and streams change their courses, and soil is built up and worn down.
A foundation of bedrock lies mostly hidden under much of what we see as we look out over the landscape of Stephenson County. The bedrock of the county is covered by a relatively thin layer of soil, and in a few places the rock is exposed in roadcuts or stream-sculpted bluffs, explains Steve Simpson, geography and geology teacher at Highland Community College, writing about the geology of the watershed in the book, Pecatonica River Watershed: Knowing the Past, Creating the Future (August 2000, Natural Land Institute, Rockford, and Cultural Waters, Inc.) Simpson reports that all of the bedrock exposed in the Pecatonica Watershed belongs to the family of rocks called sedimentary, composed of particles of pre-existing rock materials deposited in layers.  Our soil is made – one inch in 500 years according to the USDA/NRCS – from particles of this rock mixed with dead plant and animal materials.
“Rocks at or near the surface in the Sugar-Pecatonica watershed were deposited over a span of about 90 million years during a period of time 500-410 million years ago.” Simpson points out that we find fossils in these rocks because, at the time the layers of rock were formed, a huge sea teaming with creatures whose shells accumulated in these layers covered this area. We may refer to this rock as limestone, but it is really dolomite or dolostone – originally limestone, but altered by magnesium-rich seawater over time. Other kinds of rocks, pebbles, or boulders, you may find on the surface of the land or in streambeds, have been carried into the region by glaciers and streams very recently – geologically speaking.
About 286-245 million years ago, as the region gently rose and the sea level gradually fell, the land of the Upper Midwest changed from being deposited to being eroded. “And as rain fell upon the nearly flat expanse of sedimentary rock, stream channels began to form as runoff found a course back to the sea. One of the channels that began to form at that time was the ancestral Pecatonica.” (Simpson)
When we think about geography we can only stand in awe of the changes in the earth’s surface that have happened over millions of years to bring us the landscape we see today. Now, in short periods of time with large earth-moving equipment, we can make impressive changes on the surface of the land. We need to consider that each change affects soil and water – we are rearranging our earth.
 The information in this article originally appeared in the Journal-Standard in November of 2000.

Della Moen, Earth Team Volunteer, NRCS/Stephenson Soil and Water
Conservation District, an equal opportunity provider and employer, 03/26/08
(for publication on 04/05/08 in the Journal-Standard, Freeport, Illinois).
Della can be reached at info@stephensonswcd.org