The Three Forks 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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Three Forks’s center stands about 4,080 ft above sea level. Within three miles the land runs from 4,050 ft to 4,390 ft, a difference of 340 ft: rolling country. The highest named summit within 15 miles is High Peak, about 5,560 ft, 12 miles north-northeast.
Under the town center the state geologic map shows Gravel, from the Pleistocene to Holocene, less than 1.8 million years old.
The section below crosses 10 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 17×. 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: Pleistocene to Holocene, less than 1.8 million years old. About 7 mi of the line.
Siltstone, sedimentary-breccia, conglomerate. Age: Early Eocene to Early Miocene, 16 to 56 million years old. About 7 mi of the line.
Sandstone, limestone, shale. Age: Middle Jurassic to Early Cretaceous, 100 to 172 million years old. About 3 mi of the line.
Limestone, dolostone, black-shale. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 3 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 2 mi of the line.
Gneiss. Age: Archean. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 4 smaller units 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 Three Forks reaches the Gulf of America by way of the Madison, the Missouri and the Mississippi: about 3,480 river miles.
Lakes on the way: Lake Oahe, Lake Sakakawea, Lake Fort Peck and Lake Sharpe.
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 Three Forks; river miles along the main stem, rounded.
