The Shape of Salt Creek

by Carl Strang

Back when my office was at Fullersburg Woods, I had two occasions to study old maps and aerial photos of that forest preserve. Both when looking at the history of periodical cicadas in DuPage County, and when examining Fullersburg’s archeology, I found myself comparing original survey maps from the first half of the 19th Century to the 1874 county atlas to the earliest aerial photos from 1939. Though not central to these investigations, I couldn’t help but notice inconsistencies among these maps and photos in the shape of Salt Creek. Let’s begin with the 1939 aerial photo and work back.

Salt Creek enters Fullersburg in the upper left (NW) portion of the photo when it passes beneath 31st Street. The stream proceeds south, with the interruption of a small hairpin turn, before turning east. After a significant straightaway the stream turns back north, takes a big swing east and divides to surround Willow Island as it begins a long stretch flowing south, then turns SE until it exits the preserve soon after passing beneath York Road. Salt Creek today has essentially the same configuration. Let’s look next at the 1874 atlas.

For the most part Salt Creek looks similar to its present day configuration. There is one significant exception, however. In the next image I superimpose the 1874 map onto the 1939 photo.

The red line I have added to reconcile the two versions. It makes sense. That line traces the bottom edge of a sharp bluff, the edge of the Tinley Moraine. The following photo shows where one end of the adjacent lowland, cut off as the red line shows, meets the morainal bluff.

It appears that the streambed migrated between 1874 and 1939 to create that low peninsula. The concrete slab in the photo, part of an abandoned trail installed during the Great Depression by the Civilian Conservation Corps, bridges what is left of the 1874 channel. Now let’s shift to pre-1850, when the original land survey gives us the first record of Salt Creek’s shape.

This surveyor’s sketch map is based on an original 1822 record. This is significantly different from the later map and photo. Again I superimpose.

The red line again reconciles the two, and again it makes sense. The area along the red line is low, and in fact at times of flood, water sheet-flows through there, short-cutting across the base of the river bend (though most continues to follow the main channel).

What brought this back to mind was an observation I made recently, something I hadn’t noticed before, when looking at the original survey notes associated with the earliest map. The surveyor noted that the width of Salt Creek up and down the stretch now part of Fullersburg was 20-30 links. A link in the surveyor’s standard measuring chain was only 8 inches long, so that Salt Creek prior to American settlement was only around 15 feet wide. Today it’s much wider.

The 1800 width of the stream was closer to that of the central channel through the ice in this photo than to today’s banks. The picture I am left with is of a relatively small stream, wandering over the low area between the Tinley and Valparaiso Moraines. As DuPage County became agricultural, then urban, increased runoff ballooned Salt Creek’s width and volume. The growing stream carved a channel that has become more stable. The change between 1874 and today suggests that Salt Creek at least began to cut its way back to the early-1850’s channel route. However, downward erosion may have set the main channel in a shape that will resist future alteration.

Union Township, 1830’s

by Carl Strang

Yesterday I began to recount my study of what my home township in Indiana was like in the 1830’s, before Americans began to transform it from wilderness to a predominantly agricultural landscape. Here is a more detailed line drawing of the final map.

Union_Township_presettlement_vegetation

The surveyors’ description provided enough information for me to rough out the map. Getting to the final version required another step. I acquired a soils map of Marshall County, and looked for correlations between soil types and vegetation categories as the surveyors described them. A specialist might have done it differently, but for my part I was satisfied that the correlations were good enough to draw the detailed boundaries of vegetation areas by combining the surveyors’ records with the finer-scale soils map.

Of the various communities defined by woody plants, swamps are the ones most absent from today’s Union Township. The characteristic swamp tree was the tamarack. Here is some foliage of that species, which is unusual in that it is a deciduous conifer.

Tamarack foliage b

I remember seeing a tamarack tree at the old state fish hatchery that was formed out of the south end of Moore Lake, but that tree died years ago and I know of none surviving in the township today. There are bits of shrub swamps here and there.

A relatively moist (mesic) forest occupied much of the east half of the township, on the rolling Maxinkuckee Moraine. Sugar maples and beeches were characteristic trees, though not necessarily the dominant ones. A remnant of this forest is preserved by the Culver Military Academy in its Bird Sanctuary.

Dry forests and savannas were dominated by oaks and hickories, which grew on more sandy soils. They represent a continuum, with the forests shading the ground fully in the summer and the savannas’ trees scattered enough that prairie-like vegetation grew between them. A forest of this type was the site of the town now known as Culver. Gradually over my lifetime I have noted the passing, one by one, of the town’s largest surviving old oaks that were part of that forest. Dry forests persist mainly in the many “wood lots” preserved by the township’s farmers.

I am grateful to all the individuals and organizations, from private landowners to The Nature Conservancy, who have made the commitment to preserve and restore these reminders of the wilderness that once was.

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