The Cairo 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.
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Cairo’s center stands about 1,020 ft above sea level. Within three miles the land runs from 990 ft to 1,040 ft, a difference of 50 ft: nearly flat ground.
Under the town center the state geologic map shows Granitic orthogneiss and migmatite (orthogneiss, migmatite), from the Paleoarchean to Mesoarchean, 2.8 to 3.6 billion years old.
The section below crosses 4 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.
Orthogneiss, migmatite. Age: Paleoarchean to Mesoarchean, 2.8 to 3.6 billion years old. About 14 mi of the line.
Orthogneiss. Age: Paleoarchean to Mesoarchean, 2.8 to 3.6 billion years old. About 7 mi of the line.
Conglomerate, sandstone, mudstone. Age: Late Cretaceous, 72 to 100 million years old. About 2 mi of the line.
Granitic. Age: Neoarchean, 2.5 to 2.8 billion years old. About 0.8 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 Cairo reaches the Gulf of America by way of Fort Ridgely Creek, the Minnesota and the Mississippi: about 2,010 river miles.
Lake on the way: Lake Pepin.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Cairo; river miles along the main stem, rounded.
