The O'Fallon 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.
Sunny
Partly cloudy; warmer
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7° on Nov. 17, 1959, the coldest reading for this week of the year since 1948. Next is 8° in 2019.
O'Fallon’s center stands about 550 ft above sea level. Within three miles the land runs from 470 ft to 650 ft, a difference of 180 ft: gently rolling country.
Under the town center the state geologic map shows Shelburn-Patoka Formations undivided (shale, limestone), from the Late Pennsylvanian, 304 to 307 million years old.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale, limestone. Age: Late Pennsylvanian, 304 to 307 million years old. About 24 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 O'Fallon reaches the Gulf of America by way of Engle Creek, Silver Creek, the Kaskaskia and the Mississippi: about 1,160 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of O'Fallon; river miles along the main stem, rounded.
O'Fallon has a humid subtropical climate. Summer afternoons average 90° in July; winter nights fall to about 24° in January. A normal year brings about 11 inches of snow; with the rain, that comes to about 43 inches of water.
On November 14 O'Fallon normally reaches 59° and falls to 37°. The record high is 82°, in 1999; the record low 11°, in 1986. The most rain on this date, 3.23 in, fell in 1993.
Normals 1991–2020 and records since 1948 at Belleville Siu Research, 6 miles southeast, 120 ft lower. NOAA, through RCC-ACIS.
