The Flynn 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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Flynn’s center stands about 800 ft above sea level. Within three miles the land runs from 770 ft to 830 ft, a difference of 60 ft: nearly flat ground.
Under the town center the state geologic map shows Marshall Sandstone, from the Carboniferous, 324 to 359 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.
Sandstone. Age: Carboniferous, 324 to 359 million years old. About 19 mi of the line.
Shale. Age: Carboniferous, 324 to 359 million years old. About 5 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 Flynn reaches Lake Huron by way of the South Branch Cass, the Cass and the Saginaw: about 110 river miles. From there it moves on through the Great Lakes, over Niagara Falls and down the St. Lawrence to the Atlantic.
60 miles of the trip are on the Cass.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Flynn; river miles along the main stem, rounded.
