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.
Sunny
Partly cloudy; warmer
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3.25 inches of rain fell in two days, the most for this week of the year since records began in 1892. The next wettest, 2.92 inches, fell in 2003.
Alton’s center stands about 470 ft above sea level. Within three miles the land runs from 400 ft to 640 ft, a difference of 240 ft: rolling country.
Under the town center the state geologic map shows St. Louis Limestone, from the Middle Mississippian, 331 to 347 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 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.
Limestone. Age: Middle Mississippian, 331 to 347 million years old. About 6 mi of the line.
Limestone. Age: Middle Mississippian, 331 to 347 million years old. About 5 mi of the line.
Limestone, sandstone, shale. Age: Middle Mississippian, 331 to 347 million years old. About 5 mi of the line.
Clay, silt, sand. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Shale, sandstone. Age: Early Pennsylvanian to Middle Pennsylvanian, 307 to 324 million years old. About 3 mi of the line.
Limestone. Age: Middle Mississippian, 331 to 347 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 Alton reaches the Gulf of America by way of the Mississippi: about 1,170 river miles.
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 87° in July; winter nights fall to about 22° in January. About 42 inches of rain fall in a normal year.
On November 14 Alton normally reaches 55° and falls to 37°. The record high is 77°, in 1999; the record low 11°, in 1986. The most rain on this date, 1.56 in, fell in 1993.
Normals 1991–2020 and records since 1892 at Alton - Melvin Price L&D, 3 miles southeast. NOAA, through RCC-ACIS.
