The Mammoth 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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Mammoth’s center stands about 6,050 ft above sea level. Within three miles the land runs from 5,770 ft to 9,440 ft, a difference of 3,670 ft: mountain country. The highest named summit within 15 miles is Hollowtop Mountain, about 10,590 ft, 4 miles south.
Under the town center the state geologic map shows Quartzofeldspathic gneiss, from the Archean.
The section below crosses 14 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 3×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Gneiss. Age: Archean. About 9 mi of the line.
Granitic. Age: Cretaceous, 66 to 145 million years old. About 4 mi of the line.
Dolostone, limestone, sandstone. Age: Late Mississippian to Permian, 252 to 331 million years old. About 2 mi of the line.
Conglomerate, sandstone, siltstone. Age: Early Miocene to Pliocene, 2.6 to 20 million years old. About 2 mi of the line.
Age: Archean. About 1 mi of the line.
Andesite, latite. Age: Late Cretaceous, 72 to 84 million years old. 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. 8 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 Mammoth reaches the Gulf of America by way of the South Boulder, the Jefferson, the Missouri and the Mississippi: about 3,520 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 Mammoth; river miles along the main stem, rounded.
