The Illinois City 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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74° on Nov. 11, 2022, the hottest reading for this week of the year since 1940. Next is 71° in 2012.
Illinois City’s center stands about 770 ft above sea level. Within three miles the land runs from 540 ft to 770 ft, a difference of 230 ft: rolling country.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 62×. 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, sandstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 7 mi of the line.
Shale, sandstone. Age: Early Pennsylvanian, 315 to 324 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.
Limestone, dolostone. Age: Middle Devonian to Late Devonian, 374 to 388 million years old. About 4 mi of the line.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 2 mi of the line.
Shale. Age: Middle Devonian to Late Devonian, 359 to 388 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit along the line are not listed.
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 Illinois City reaches the Gulf of America by way of the Mississippi: about 1,440 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Illinois City; river miles along the main stem, rounded.
Illinois City has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 13° in January. About 36 inches of rain fall in a normal year.
Normals 1991–2020 and records since 1940 at Illinois City Dam 16, 6 miles west-northwest, 220 ft lower. NOAA, through RCC-ACIS.
