The Alton 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
Mostly sunny; warmer
Mostly sunny
Partly cloudy
Partly cloudy
Mostly sunny
Showers likely
75° on Nov. 13, 1999, the hottest reading for this week of the year since 1899. Next is 74° in 2001.
Alton’s center stands about 1,320 ft above sea level. Within three miles the land runs from 1,270 ft to 1,440 ft, a difference of 170 ft: gently rolling country.
Under the town center the state geologic map shows Dakata and Windrow Formations (sandstone, shale), from the Early Cretaceous to Late Cretaceous, 94 to 113 million years old.
The section below crosses 2 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 19 mi of the line.
Shale. Age: Late Cretaceous, 90 to 100 million years old. About 5 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 Alton reaches the Gulf of America by way of the Floyd, the Missouri and the Mississippi: about 1,940 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 Alton; river miles along the main stem, rounded.
Alton has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 9° in January. A normal year brings about 35 inches of snow; with the rain, that comes to about 30 inches of water.
On November 14 Alton normally reaches 46° and falls to 26°. The record high is 71°, in 2025; the record low −20°, in 1959. The most rain on this date, 1.35 in, fell in 1926.
Normals 1991–2020 and records since 1899 at Sioux Center 2 SE, 9 miles west-northwest. NOAA, through RCC-ACIS.
