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
Mostly sunny
Sunny
Mostly sunny
Mostly sunny
Mostly sunny
Alton’s center stands about 430 ft above sea level. Within three miles the land runs from 390 ft to 800 ft, a difference of 410 ft: hilly country. The highest named summit within 15 miles is Pilot Knob, about 960 ft, 13 miles north-northeast.
Under the town center the state geologic map shows Blue River Group (limestone), from the Carboniferous, 324 to 359 million years old.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 38×. 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. Age: Carboniferous, 324 to 359 million years old. About 6 mi of the line.
Sandstone, limestone. Age: Carboniferous, 324 to 359 million years old. About 4 mi of the line.
Sandstone, shale. Age: Carboniferous, 324 to 359 million years old. About 4 mi of the line.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 3 mi of the line.
Shale, sandstone. Age: Carboniferous, 299 to 324 million years old. About 2 mi of the line.
Limestone, sandstone. Age: Carboniferous, 324 to 359 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. 3 smaller units along the line are not listed.
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 Ohio and the Mississippi: about 1,270 river miles.
970 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.
