The Dorchester 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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Dorchester’s center stands about 660 ft above sea level. Within three miles the land runs from 610 ft to 670 ft, a difference of 60 ft: nearly flat ground.
Under the town center the state geologic map shows Shelburn-Patoka Formations undivided (shale, limestone), from the Late Pennsylvanian, 304 to 307 million years old.
The section below crosses 2 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.
Shale, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 17 mi of the line.
Shale, sandstone, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 7 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 Dorchester reaches the Gulf of America by way of West Fork Cahokia Creek, Cahokia Creek and the Mississippi: about 1,200 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Dorchester; river miles along the main stem, rounded.
