The Dillon 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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−31° on Nov. 16, 1955, the coldest reading for this week of the year since 1895. Next is −30° in 1959.
Dillon’s center stands about 5,090 ft above sea level. Within three miles the land runs from 5,030 ft to 5,680 ft, a difference of 650 ft: hilly country. The highest named summit within 15 miles is Benson Peak, about 8,460 ft, 11 miles southeast.
Under the town center the state geologic map shows Alluvium (gravel, sand, silt), 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 6×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sedimentary. Age: Tertiary, 2.6 to 66 million years old. About 11 mi of the line.
Siltstone, sandstone, shale. Age: Early Triassic to Early Cretaceous, 100 to 252 million years old. About 2 mi of the line.
Gneiss. Age: Archean. About 2 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 2 mi of the line.
Volcanic. Age: Middle Eocene, 41 to 48 million years old. About 2 mi of the line.
Age: Archean. About 2 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 Dillon reaches the Gulf of America by way of the Beaverhead, the Jefferson, the Missouri and the Mississippi: about 3,600 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 Dillon; river miles along the main stem, rounded.
Dillon has a cold semi-arid climate. Summer afternoons average 83° in July; winter nights fall to about 13° in December. A normal year brings about 11 inches of snow; with the rain, that comes to about 11 inches of water.
On November 14 Dillon normally reaches 42° and falls to 22°. The record high is 66°, in 1906; the record low −10°, in 1978. The most rain on this date, 0.30 in, fell in 1911.
Normals 1991–2020 and records since 1895 at Dillon U Of Montana Western, here. NOAA, through RCC-ACIS.
