The Irwin 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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75° on Nov. 14, 1999, the hottest reading for this week of the year since 1887. Next is 74° in 1989.
Irwin’s center stands about 660 ft above sea level. Within three miles the land runs from 630 ft to 720 ft, a difference of 90 ft: gently rolling country.
Under the town center the state geologic map shows Silurian System undivided (dolostone, limestone), from the Silurian, 422 to 445 million years old.
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.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 24 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 Irwin reaches the Gulf of America by way of Gar Creek, the Kankakee, the Illinois and the Mississippi: about 1,510 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 Irwin; river miles along the main stem, rounded.
Irwin has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 16° in January. A normal year brings about 21 inches of snow; with the rain, that comes to about 42 inches of water.
On November 14 Irwin normally reaches 50° and falls to 33°. The record high is 75°, in 1999; the record low 5°, in 1986. The most rain on this date, 0.56 in, fell in 1985.
Normals 1991–2020 and records since 1887 at Kankakee Wwtp, 8 miles northeast. NOAA, through RCC-ACIS.
