The Decorah 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. 13, 1999, the hottest reading for this week of the year since 1893. Next is 73° in 1953.
Decorah’s center stands about 870 ft above sea level. Within three miles the land runs from 830 ft to 1,190 ft, a difference of 360 ft: rolling country.
Under the town center the state geologic map shows Galena Group and Platteville Formation (dolostone, limestone), from the Late Ordovician, 447 to 459 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 40×. 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, sandstone. Age: Early Ordovician to Late Ordovician, 454 to 487 million years old. About 10 mi of the line.
Shale, dolostone. Age: Late Ordovician, 447 to 454 million years old. About 8 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 4 mi of the line.
Dolostone, limestone. Age: Middle Devonian, 384 to 394 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 Decorah reaches the Gulf of America by way of the Upper Iowa and the Mississippi: about 1,710 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Decorah; river miles along the main stem, rounded.
Decorah has a hot-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 10° in January. A normal year brings about 38 inches of snow; with the rain, that comes to about 38 inches of water.
On November 14 Decorah normally reaches 47° and falls to 29°. The record high is 71°, in 2025; the record low −7°, in 1916. The most rain on this date, 1.08 in, fell in 1902.
Normals 1991–2020 and records since 1893 at Decorah, here. NOAA, through RCC-ACIS.
