The Decatur 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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80° on Nov. 14, 1999, the hottest reading for this week of the year since 1897. Next is 76° in 2025.
Decatur’s center stands about 1,130 ft above sea level. Within three miles the land runs from 930 ft to 1,130 ft, a difference of 200 ft: rolling country.
Under the town center the state geologic map shows Bronson Group (limestone, shale), from the Middle Pennsylvanian to Late Pennsylvanian, 299 to 315 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.
Limestone, shale. Age: Middle Pennsylvanian to Late Pennsylvanian, 299 to 315 million years old. About 13 mi of the line.
Shale, siltstone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 7 mi of the line.
Limestone, shale. Age: Late Pennsylvanian, 299 to 307 million years old. About 3 mi of the line.
Shale, limestone. Age: Middle Pennsylvanian, 307 to 315 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 Decatur reaches the Gulf of America by way of Britton Branch, the Weldon, the Thompson, the Grand River, the Missouri and the Mississippi: about 1,560 river miles.
1,170 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Decatur; river miles along the main stem, rounded.
Decatur has a hot-summer humid continental climate. Summer afternoons average 87° in July; winter nights fall to about 14° in January. A normal year brings about 27 inches of snow; with the rain, that comes to about 41 inches of water.
On November 14 Decatur normally reaches 51° and falls to 30°. The record high is 80°, in 1999; the record low 2°, in 1940. The most rain on this date, 1.56 in, fell in 1931.
Normals 1991–2020 and records since 1897 at Lamoni, 10 miles south-southwest. NOAA, through RCC-ACIS.
