The St. Onge 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.
Partly cloudy
Sunny
Mostly sunny
Partly cloudy
Partly cloudy; cooler
Partly cloudy
Showers likely
−23° on Nov. 16, 1959, the coldest reading for this week of the year since 1893. Next is −15° in 1916.
St. Onge’s center stands about 3,430 ft above sea level. Within three miles the land runs from 3,310 ft to 3,870 ft, a difference of 560 ft: hilly country. The highest named summit within 15 miles is Bald Mountain, about 6,600 ft, 15 miles south-southwest.
Under the town center the state geologic map shows Alluvium (coarse-detrital, fine-detrital), from the Quaternary, less than 2.6 million years old.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 8×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, siltstone. Age: Early Cretaceous, 100 to 145 million years old. About 5 mi of the line.
Coarse-detrital, fine-detrital. Age: Quaternary, less than 2.6 million years old. About 4 mi of the line.
Limestone, dolostone. Age: Late Devonian to Early Mississippian, 347 to 384 million years old. About 2 mi of the line.
Sandstone, siltstone, claystone. Age: Middle Jurassic to Late Jurassic, 145 to 175 million years old. About 2 mi of the line.
Black-shale. Age: Late Cretaceous, 66 to 100 million years old. About 2 mi of the line.
Claystone, conglomerate, sandstone. Age: Early Cretaceous, 100 to 145 million years old. 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. 7 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 St. Onge reaches the Gulf of America by way of Dry Creek, False Bottom Creek, Redwater Creek, the Belle Fourche, the Cheyenne, the Missouri and the Mississippi: about 2,570 river miles.
Lakes on the way: Lake Oahe, Lake Sharpe, Lake Francis Case and Lewis and Clark Lake.
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 St. Onge; river miles along the main stem, rounded.
St. Onge has a warm-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 16° in January. A normal year brings about 70 inches of snow; with the rain, that comes to about 21 inches of water.
On November 14 St. Onge normally reaches 46° and falls to 26°. The record high is 76°, in 1894; the record low −20°, in 1959. The most rain on this date, 2.67 in, fell in 1944.
Normals 1991–2020 and records since 1893 at Spearfish, 8 miles west-southwest, 200 ft higher. NOAA, through RCC-ACIS.
