The Union 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.
Sunny
Partly cloudy; warmer
Mostly sunny
Partly cloudy
Partly cloudy
Mostly sunny
Showers likely
−7° on Nov. 12, 2019, the coldest reading for this week of the year since 1996. Next is 2° in 2005.
Union’s center stands about 930 ft above sea level. Within three miles the land runs from 910 ft to 1,050 ft, a difference of 140 ft: gently rolling country.
Under the town center the state geologic map shows Gilmore City Formation (limestone), from the Early Mississippian to Middle Mississippian, 331 to 359 million years old.
The section below crosses 5 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: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 8 mi of the line.
Dolostone, limestone, siltstone. Age: Early Mississippian, 347 to 359 million years old. About 7 mi of the line.
Limestone. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 6 mi of the line.
Shale, sandstone, siltstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 2 mi of the line.
Dolostone, limestone. Age: Middle Mississippian to Late Mississippian, 324 to 347 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 Union reaches the Gulf of America by way of the Iowa and the Mississippi: about 1,630 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Union; river miles along the main stem, rounded.
Union has a dry-winter hot-summer continental climate. Summer afternoons average 83° in July; winter nights fall to about 10° in January. About 33 inches of rain fall in a normal year.
On November 14 Union normally reaches 47° and falls to 27°. The record high is 72°, in 2025; the record low 8°, in 2019.
Normals 1991–2020 and records since 1996 at Marshalltown Municipal Airport, 12 miles southeast. NOAA, through RCC-ACIS.
