The Grand Detour 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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0° on Nov. 17, 1959, the coldest reading for this week of the year since 1893. Next is 2° in 2019.
Grand Detour’s center stands about 700 ft above sea level. Within three miles the land runs from 640 ft to 830 ft, a difference of 190 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 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: Late Ordovician, 454 to 459 million years old. About 8 mi of the line.
Sandstone, limestone, dolostone. Age: Middle Ordovician to Late Ordovician, 454 to 468 million years old. About 8 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 7 mi of the line.
Shale, sandstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 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.
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 Grand Detour reaches the Gulf of America by way of the Rock River and the Mississippi: about 1,550 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grand Detour; river miles along the main stem, rounded.
Grand Detour has a hot-summer humid continental climate. Summer afternoons average 83° in July; winter nights fall to about 14° in January. A normal year brings about 31 inches of snow; with the rain, that comes to about 40 inches of water.
On November 14 Grand Detour normally reaches 48° and falls to 31°. The record high is 75°, in 1971; the record low 5°, in 1986. The most rain on this date, 1.60 in, fell in 1926.
Normals 1991–2020 and records since 1893 at Dixon Wwtp, 7 miles southwest. NOAA, through RCC-ACIS.
