The Arnold 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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85° on Nov. 11, 1989, the hottest reading for this week of the year since 1874. Next is 83° in 2016.
Arnold’s center stands about 580 ft above sea level. Within three miles the land runs from 390 ft to 730 ft, a difference of 340 ft: rolling country. The highest named summit within 15 miles is Frisco Hill, about 860 ft, 5 miles southwest.
Under the town center the state geologic map shows Meramecian Series (limestone), from the Carboniferous, 324 to 359 million years old.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 33×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 8 mi of the line.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 6 mi of the line.
Limestone. Age: Middle Mississippian, 331 to 347 million years old. About 4 mi of the line.
Limestone. Age: Middle Ordovician, 459 to 471 million years old. About 3 mi of the line.
Limestone. Age: Middle Mississippian, 331 to 347 million years old. About 2 mi of the line.
Limestone. Age: Middle Ordovician to Late Ordovician, 445 to 471 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. 3 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 Arnold reaches the Gulf of America by way of Pomme Creek, the Meramec and the Mississippi: about 1,140 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Arnold; river miles along the main stem, rounded.
Arnold has a hot-summer humid continental climate. Summer afternoons average 90° in July; winter nights fall to about 24° in January. A normal year brings about 17 inches of snow; with the rain, that comes to about 42 inches of water.
On November 14 Arnold normally reaches 56° and falls to 38°. The record high is 81°, in 1971; the record low 13°, in 1940. The most rain on this date, 1.86 in, fell in 1993.
Normals 1991–2020 and records since 1874 from the St Louis Area threaded record (St Louis Lambert International Airport, 22 miles north). NOAA, through RCC-ACIS.
