The Grantfork 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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Grantfork’s center stands about 530 ft above sea level. Within three miles the land runs from 500 ft to 610 ft, a difference of 110 ft: gently rolling country.
Under the town center the state geologic map shows Bond Formation (shale, sandstone, 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, sandstone, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 18 mi of the line.
Shale, 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 Grantfork reaches the Gulf of America by way of East Fork Silver Creek, Silver Creek, the Kaskaskia and the Mississippi: about 1,180 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grantfork; river miles along the main stem, rounded.
