The Thermopolis 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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77° on Nov. 15, 1941, the hottest reading for this week of the year since 1899. Next is 74° in 1999.
Thermopolis’s center stands about 4,340 ft above sea level. Within three miles the land runs from 4,300 ft to 5,120 ft, a difference of 820 ft: hilly country. The highest named summit within 15 miles is Stagner Mountain, about 7,540 ft, 13 miles south.
Under the town center the state geologic map shows Alluvium and Colluvium (clay, silt, sand), from the Pleistocene to Holocene, less than 2.6 million years old.
The section below crosses 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Clay, silt, sand. Age: Pleistocene to Holocene, less than 2.6 million years old. About 7 mi of the line.
Black-shale, sandstone, dolostone. Age: Permian, 252 to 299 million years old. About 6 mi of the line.
Shale, siltstone. Age: Late Cretaceous, 78 to 83 million years old. About 5 mi of the line.
Sandstone, shale. Age: Late Cretaceous, 66 to 100 million years old. About 2 mi of the line.
Sandstone, dolostone, shale. Age: Carboniferous to Permian, 252 to 359 million years old. About 1 mi of the line.
Sandstone, shale. Age: Late Cretaceous, 66 to 100 million years old. About 0.9 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 5 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 Thermopolis reaches the Gulf of America by way of the Bighorn, the Yellowstone, the Missouri and the Mississippi: about 3,310 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 Thermopolis; river miles along the main stem, rounded.
Thermopolis has a cold semi-arid climate. Summer afternoons average 92° in July; winter nights fall to about 12° in January. A normal year brings about 27 inches of snow; with the rain, that comes to about 12 inches of water.
On November 14 Thermopolis normally reaches 49° and falls to 22°. The record high is 71°, in 1999; the record low −14°, in 1959. The most rain on this date, 0.84 in, fell in 1991.
Normals 1991–2020 and records since 1899 at Thermopolis, here. NOAA, through RCC-ACIS.
