The Boneau 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
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Showers likely; cooler
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77° on Nov. 12, 1999, the hottest reading for this week of the year since 1921. Next is 73° in 2025.
Boneau’s center stands about 3,310 ft above sea level. Within three miles the land runs from 2,990 ft to 3,990 ft, a difference of 1,000 ft: steep hill country. The highest named summit within 15 miles is Baldy Mountain, about 6,890 ft, 14 miles southeast.
Under the town center the state geologic map shows Judith River Formation (sandstone, shale), from the Late Cretaceous, 72 to 84 million years old.
The section below crosses 7 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.
Sandstone, shale. Age: Late Cretaceous, 72 to 84 million years old. About 9 mi of the line.
Shale. Age: Late Cretaceous, 72 to 84 million years old. About 6 mi of the line.
Mafic-volcanic. Age: Tertiary, 2.6 to 66 million years old. About 4 mi of the line.
Syenitic, syenite. Age: Tertiary, 2.6 to 66 million years old. About 3 mi of the line.
Age: Tertiary, 2.6 to 66 million years old. About 0.9 mi of the line.
Sandstone, shale, bentonite. Age: Late Cretaceous, 66 to 84 million years old. About 0.7 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 Boneau reaches the Gulf of America by way of Boxelder Creek, Big Sandy Creek, the Milk River, the Missouri and the Mississippi: about 3,410 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 Boneau; river miles along the main stem, rounded.
Boneau has a cold semi-arid climate. Summer afternoons average 86° in July; winter nights fall to about 10° in January. About 13 inches of rain fall in a normal year.
On November 14 Boneau normally reaches 44° and falls to 22°. The record high is 72°, in 1999; the record low −22°, in 2014. The most rain on this date, 0.39 in, fell in 1927.
Normals 1991–2020 and records since 1921 at Big Sandy, 14 miles southwest, 540 ft lower. NOAA, through RCC-ACIS.
