The Longmont 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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−14° on Nov. 11, 1950, the coldest reading for this week of the year since 1893. Next is −13° in 1916.
Longmont’s center stands about 4,990 ft above sea level. Within three miles the land runs from 4,900 ft to 5,100 ft, a difference of 200 ft: gently rolling country. The highest named summit within 15 miles is Fairview Peak, about 8,500 ft, 13 miles west.
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 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.
Sand, silt. Age: Quaternary, less than 2.6 million years old. About 7 mi of the line.
Unconsolidated. Age: Quaternary, less than 2.6 million years old. About 6 mi of the line.
Shale. Age: Late Cretaceous, 66 to 100 million years old. About 5 mi of the line.
Shale. Age: Late Cretaceous, 66 to 100 million years old. About 1 mi of the line.
Arkose, conglomerate. Age: Carboniferous to Permian, 252 to 324 million years old. About 1 mi of the line.
Sandstone, shale, limestone. Age: Permian to Early Triassic, 247 to 299 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. 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 Longmont reaches the Gulf of America by way of Saint Vrain Creek, the South Platte, the Platte, the Missouri and the Mississippi: about 2,370 river miles.
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 Longmont; river miles along the main stem, rounded.
Longmont has a cold semi-arid climate. Summer afternoons average 91° in July; winter nights fall to about 14° in January. About 15 inches of rain fall in a normal year.
On November 14 Longmont normally reaches 54° and falls to 24°. The record high is 78°, in 1999; the record low −6°, in 1940. The most rain on this date, 0.79 in, fell in 1994.
Normals 1991–2020 and records since 1893 at Longmont 2 ESE, here. NOAA, through RCC-ACIS.
