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.
Partly cloudy
Partly cloudy; warmer
Sunny
Partly cloudy
Mostly sunny
Mostly sunny
Mostly sunny
85° on Nov. 12, 2010, the hottest reading for this week of the year since 1940. Next is 81° in 1999.
Alton’s center stands about 740 ft above sea level. Within three miles the land runs from 700 ft to 960 ft, a difference of 260 ft: rolling country. The highest named summit within 15 miles is Mosby Hill, about 1,010 ft, 9 miles northeast.
Under the town center the state geologic map shows Smithville Dolomite, Powell Dolomite, Cotter Dolomite, Jefferson City Dolomite (dolostone), from the Early Ordovician, 471 to 487 million years old.
The section below crosses 3 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 32×. 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. Age: Early Ordovician, 471 to 487 million years old. About 20 mi of the line.
Sandstone, chert. Age: Early Ordovician, 471 to 487 million years old. About 3 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 0.4 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 Tucker Creek, Piney Creek, Frederick Creek, the Eleven Point, the Black River, the White River and the Mississippi: about 1,030 river miles.
620 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 humid subtropical climate. Summer afternoons average 88° in July; winter nights fall to about 22° in January. About 47 inches of rain fall in a normal year, with about 4 inches of snow.
On November 14 Alton normally reaches 57° and falls to 34°. The record high is 81°, in 1999; the record low 12°, in 1969. The most rain on this date, 0.63 in, fell in 1997.
Normals 1991–2020 and records since 1940 at Alton, here. NOAA, through RCC-ACIS.
