The Irwin 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.
Mostly sunny
Partly cloudy
Mostly sunny
Partly cloudy
Partly cloudy
Mostly sunny
Showers likely
−14° on Nov. 12, 2019, the coldest reading for this week of the year since 1893. Next is −7° in 1959.
Irwin’s center stands about 1,280 ft above sea level. Within three miles the land runs from 1,240 ft to 1,460 ft, a difference of 220 ft: rolling country.
Under the town center the state geologic map shows Upper Cherokee Group (shale, siltstone), from the Middle Pennsylvanian, 307 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.
Sandstone, shale. Age: Early Cretaceous to Late Cretaceous, 94 to 113 million years old. About 12 mi of the line.
Shale, limestone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 5 mi of the line.
Shale, siltstone. Age: Middle Pennsylvanian, 307 to 315 million years old. About 5 mi of the line.
Shale, sandstone, siltstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 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 Irwin reaches the Gulf of America by way of the West Nishnabotna, the Nishnabotna, the Missouri and the Mississippi: about 1,810 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 Irwin; river miles along the main stem, rounded.
Irwin has a hot-summer humid continental climate. Summer afternoons average 83° in July; winter nights fall to about 9° in January. About 35 inches of rain fall in a normal year.
On November 14 Irwin normally reaches 47° and falls to 25°. The record high is 78°, in 1999; the record low −7°, in 1959. The most rain on this date, 2.30 in, fell in 1926.
Normals 1991–2020 and records since 1893 at Audubon, 16 miles east-southeast. NOAA, through RCC-ACIS.
