The Shannon 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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72° on Nov. 11, 2022, the hottest reading for this week of the year since 1948. Next is 71° in 1989.
Shannon’s center stands about 930 ft above sea level. Within three miles the land runs from 850 ft to 1,030 ft, a difference of 180 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.
The section below crosses 4 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.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 12 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 8 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 454 to 459 million years old. About 2 mi of the line.
Shale, limestone. Age: Late Ordovician, 445 to 454 million years old. About 2 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 Shannon reaches the Gulf of America by way of Lost Creek, Yellow Creek, the Pecatonica, the Rock River and the Mississippi: about 1,700 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Shannon; river miles along the main stem, rounded.
Shannon has a hot-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 11° in January. A normal year brings about 34 inches of snow; with the rain, that comes to about 38 inches of water.
On November 14 Shannon normally reaches 47° and falls to 29°. The record high is 71°, in 1989; the record low 10°, in 1996. The most rain on this date, 2.50 in, fell in 1951.
Normals 1991–2020 and records since 1948 at Freeport Wastewater Plant, 12 miles northeast, 180 ft lower. NOAA, through RCC-ACIS.
