The Arco 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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−20° on Nov. 16, 1955, the coldest reading for this week of the year since 1914. Next is −8° in 1978.
Arco’s center stands about 5,320 ft above sea level. Within three miles the land runs from 5,260 ft to 7,120 ft, a difference of 1,860 ft: steep hill country. The highest named summit within 15 miles is King Mountain, about 10,570 ft, 10 miles north.
Under the town center the state geologic map shows Alluvial deposits (gravel, sand, silt), from the Quaternary, less than 2.6 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Basalt. Age: Late Pliocene to Pleistocene, less than 3 million years old. About 9 mi of the line.
Gravel, sand, silt. Age: Quaternary, less than 2.6 million years old. About 7 mi of the line.
Age: Carboniferous, 324 to 359 million years old. About 5 mi of the line.
Gravel. Age: Quaternary, less than 2.6 million years old. About 2 mi of the line.
Gravel, sand, silt. Age: Pliocene to Pleistocene, less than 5.3 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.
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.
Arco has a cold semi-arid climate. Summer afternoons average 86° in July; winter nights fall to about 7° in January. A normal year brings about 24 inches of snow; with the rain, that comes to about 9 inches of water.
On November 14 Arco normally reaches 43° and falls to 20°. The record high is 63°, in 1999; the record low −3°, in 1959. The most rain on this date, 0.49 in, fell in 1981.
Normals 1991–2020 and records since 1914 at Arco, here. NOAA, through RCC-ACIS.
