The Twin Bridges 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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72° on Nov. 12, 1999, the hottest reading for this week of the year since 1950. Next is 69° in 2025.
Twin Bridges’s center stands about 4,630 ft above sea level. Within three miles the land runs from 4,590 ft to 5,000 ft, a difference of 410 ft: hilly country. The highest named summit within 15 miles is Granite Peak, about 10,550 ft, 14 miles east.
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 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 3×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Unconsolidated. Age: Pleistocene to Holocene, less than 1.8 million years old. About 7 mi of the line.
Age: Late Miocene to Holocene, less than 7.2 million years old. About 5 mi of the line.
Age: Pleistocene to Holocene, less than 1.8 million years old. About 3 mi of the line.
Limestone, shale, dolostone. Age: Late Devonian to Early Mississippian, 347 to 374 million years old. About 2 mi of the line.
Gneiss. Age: Archean. About 1 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 1 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 Twin Bridges reaches the Gulf of America by way of the Beaverhead, the Jefferson, the Missouri and the Mississippi: about 3,550 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 Twin Bridges; river miles along the main stem, rounded.
Twin Bridges has a cold semi-arid climate. Summer afternoons average 85° in July; winter nights fall to about 12° in December. About 9 inches of rain fall in a normal year.
On November 14 Twin Bridges normally reaches 45° and falls to 20°. The record high is 68°, in 2021; the record low −25°, in 1959. The most rain on this date, 0.17 in, fell in 1965.
Normals 1991–2020 and records since 1950 at Twin Bridges, here. NOAA, through RCC-ACIS.
