The Ossian 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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71° on Nov. 17, 1941, the hottest reading for this week of the year since 1893. Next is 71° in 2012.
Ossian’s center stands about 1,260 ft above sea level. Within three miles the land runs from 1,090 ft to 1,270 ft, a difference of 180 ft: gently rolling country.
Under the town center the state geologic map shows Maquoketa formation (shale, dolostone), from the Late Ordovician, 447 to 454 million years old.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 43×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, dolostone. Age: Late Ordovician, 447 to 454 million years old. About 15 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 4 mi of the line.
Limestone, dolostone. Age: Middle Devonian to Late Devonian, 374 to 388 million years old. About 2 mi of the line.
Dolostone, sandstone. Age: Early Ordovician to Late Ordovician, 454 to 487 million years old. About 2 mi of the line.
Dolostone, limestone. Age: Middle Devonian, 384 to 394 million years old. About 2 mi of the line.
Limestone. Age: Silurian, 440 to 445 million years old. About 0.3 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 Ossian reaches the Gulf of America by way of the Yellow and the Mississippi: about 1,660 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Ossian; river miles along the main stem, rounded.
Ossian has a hot-summer humid continental climate. Summer afternoons average 83° in July; winter nights fall to about 7° in January. A normal year brings about 40 inches of snow; with the rain, that comes to about 39 inches of water.
On November 14 Ossian normally reaches 45° and falls to 26°. The record high is 69°, in 1990; the record low −5°, in 1916. The most rain on this date, 1.17 in, fell in 1902.
Normals 1991–2020 and records since 1893 at Postville, 11 miles east-southeast. NOAA, through RCC-ACIS.
