The Boulder 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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71° on Nov. 12, 1999, the hottest reading for this week of the year since 1880. Next is 67° in 1990.
Boulder’s center stands about 4,900 ft above sea level. Within three miles the land runs from 4,820 ft to 6,160 ft, a difference of 1,340 ft: steep hill country. The highest named summit within 15 miles is Crow Peak, about 9,390 ft, 11 miles east-northeast.
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 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 4×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granitic. Age: Cretaceous, 66 to 145 million years old. About 17 mi of the line.
Andesite, latite. Age: Late Cretaceous, 72 to 84 million years old. 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.
Limestone, dolostone, shale. Age: Late Devonian to Early Mississippian, 347 to 374 million years old. About 2 mi of the line.
Age: Pleistocene to Holocene, less than 1.8 million years old. About 1 mi of the line.
Shale, limestone, sandstone. Age: Middle Cambrian to Cambrian, 487 to 521 million years old. About 0.6 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 Boulder reaches the Gulf of America by way of the Boulder, Jefferson Slough, the Jefferson, the Missouri and the Mississippi: about 3,560 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 Boulder; river miles along the main stem, rounded.
Boulder has a cold semi-arid climate. Summer afternoons average 83° in July; winter nights fall to about 11° in December. About 11 inches of rain fall in a normal year.
On November 14 Boulder normally reaches 43° and falls to 19°. The record high is 66°, in 1999; the record low −18°, in 1959. The most rain on this date, 0.50 in, fell in 1989.
Normals 1991–2020 and records since 1880 at Boulder, here. NOAA, through RCC-ACIS.
