The Arapahoe 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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Partly cloudy
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Mostly sunny; cooler
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Chance of showers
−21° on Nov. 13, 2014, the coldest reading for this week of the year since 1907. Next is −20° in 1911.
Arapahoe’s center stands about 5,000 ft above sea level. Within three miles the land runs from 4,960 ft to 5,270 ft, a difference of 310 ft: rolling country. The highest named summit within 15 miles is Ninemile Hill, about 5,970 ft, 11 miles south-southeast.
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 3 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 21×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Claystone. Age: Eocene, 34 to 56 million years old. About 19 mi of the line.
Clay, silt, sand. Age: Pleistocene to Holocene, less than 2.6 million years old. About 4 mi of the line.
Gravel. Age: Pleistocene to Holocene, less than 2.6 million years old. About 0.5 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 Arapahoe reaches the Gulf of America by way of the Little Wind, the Wind River, the Bighorn, the Yellowstone, the Missouri and the Mississippi: about 3,380 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 Arapahoe; river miles along the main stem, rounded.
Arapahoe has a cold semi-arid climate. Summer afternoons average 88° in July; winter nights fall to about 4° in January. A normal year brings about 44 inches of snow; with the rain, that comes to about 10 inches of water.
On November 14 Arapahoe normally reaches 44° and falls to 18°. The record high is 72°, in 1909; the record low −17°, in 1959. The most rain on this date, 0.43 in, fell in 1985.
Normals 1991–2020 and records since 1907 at Riverton, 8 miles northeast. NOAA, through RCC-ACIS.
