The Iroquois plate. Relief from Copernicus GLO-30; rivers and lakes from USGS NHD; watersheds from the USGS Watershed Boundary Dataset; roads and city limits from Census TIGER 2024.
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Iroquois’s center stands about 660 ft above sea level. Within three miles the land runs from 630 ft to 700 ft, a difference of 70 ft: gently rolling country.
Under the town center the state geologic map shows New Albany Shale, Blocher Shale, Sylamore Sandstone, Selmier Shale, Sweetland Creek Shale, Grassy Creek Shale, Saverton Shale, and Louisiana Limestone, from the Middle Devonian to Late Devonian, 359 to 388 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale. Age: Middle Devonian to Late Devonian, 359 to 388 million years old. About 7 mi of the line.
Siltstone. Age: Carboniferous, 324 to 359 million years old. About 5 mi of the line.
Limestone. Age: Middle Devonian, 384 to 394 million years old. About 5 mi of the line.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 5 mi of the line.
Black-shale. Age: Devonian to Carboniferous, 324 to 422 million years old. About 3 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
Heights from Copernicus GLO-90 (a surface model: it includes buildings and tree canopy); summits from USGS GNIS; rivers from USGS NHDPlus HR; rock from the USGS State Geologic Map Compilation.
A raindrop that lands in Iroquois reaches the Gulf of America by way of the Iroquois, the Kankakee, the Illinois and the Mississippi: about 1,550 river miles.
Lake on the way: Peoria Lake.
1,190 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Iroquois; river miles along the main stem, rounded.
