The Somonauk 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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1° on Nov. 12, 2019, the coldest reading for this week of the year since 1912. Next is 3° in 1986.
Somonauk’s center stands about 690 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 Ancell Group (sandstone, limestone, dolostone), from the Middle Ordovician to Late Ordovician, 454 to 468 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 57×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone, limestone, dolostone. Age: Middle Ordovician to Late Ordovician, 454 to 468 million years old. About 11 mi of the line.
Dolostone, sandstone. Age: Middle Cambrian to Cambrian, 487 to 521 million years old. About 10 mi of the line.
Dolostone. Age: Early Ordovician to Middle Ordovician, 459 to 487 million years old. About 3 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 454 to 459 million years old. About 0.5 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 Somonauk reaches the Gulf of America by way of Buck Branch, Somonauk Creek, the Fox River, the Illinois and the Mississippi: about 1,470 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 Somonauk; river miles along the main stem, rounded.
Somonauk has a hot-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 12° in January. A normal year brings about 30 inches of snow; with the rain, that comes to about 37 inches of water.
On November 14 Somonauk normally reaches 47° and falls to 29°. The record high is 73°, in 1989; the record low 3°, in 1986. The most rain on this date, 2.42 in, fell in 1926.
Normals 1991–2020 and records since 1912 at Paw Paw 2 S, 15 miles west, 200 ft higher. NOAA, through RCC-ACIS.
