The Opheim 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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Opheim’s center stands about 3,260 ft above sea level. Within three miles the land runs from 3,050 ft to 3,280 ft, a difference of 230 ft: rolling country.
Under the town center the state geologic map shows Paleosol (silt), from the Pleistocene, less than 2.6 million years old.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 31×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Age: Late Miocene to Pliocene, 2.6 to 12 million years old. About 8 mi of the line.
Silt. Age: Pleistocene, less than 2.6 million years old. About 8 mi of the line.
Shale. Age: Late Cretaceous, 72 to 84 million years old. About 3 mi of the line.
Sandstone, siltstone, black-shale. Age: Late Cretaceous, 66 to 84 million years old. About 2 mi of the line.
Sandstone, shale, bentonite. Age: Late Cretaceous, 66 to 84 million years old. About 2 mi of the line.
Sandstone, shale. Age: Early Paleocene to Middle Paleocene, 59 to 66 million years old. About 0.7 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit along the line are not listed.
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 Opheim reaches the Gulf of America by way of Middle Fork Porcupine Creek, Porcupine Creek, the Milk River, the Missouri and the Mississippi: about 3,020 river miles.
Lakes on the way: Lake Oahe, Lake Sakakawea, Lake Sharpe and Lake Francis Case.
1,170 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Opheim; river miles along the main stem, rounded.
