The St. Clair 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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St. Clair’s center stands about 740 ft above sea level. Within three miles the land runs from 550 ft to 840 ft, a difference of 290 ft: rolling country.
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 41×. 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, chert. Age: Early Ordovician, 471 to 487 million years old. About 13 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 7 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 3 mi of the line.
Shale, limestone, sandstone. Age: Carboniferous, 299 to 324 million years old. About 2 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 St. Clair reaches the Gulf of America by way of Happy Sock Creek, the Bourbeuse, the Meramec and the Mississippi: about 1,220 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of St. Clair; river miles along the main stem, rounded.
