The Prairie du Rocher 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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86° on Nov. 14, 1999, the hottest reading for this week of the year since 1974. Next is 85° in 1989.
Prairie du Rocher’s center stands about 390 ft above sea level. Within three miles the land runs from 370 ft to 700 ft, a difference of 330 ft: rolling country. The highest named summit within 15 miles is Pikes Peak, about 750 ft, 10 miles southwest.
Under the town center the state geologic map shows Warsaw Formation and Salem Limestone, from the Middle Mississippian, 331 to 347 million years old.
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 36×. 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, sandstone, shale. Age: Middle Mississippian, 331 to 347 million years old. About 9 mi of the line.
Limestone, sandstone, shale. Age: Late Mississippian, 324 to 331 million years old. About 2 mi of the line.
Limestone, dolostone. Age: Late Ordovician, 447 to 454 million years old. About 2 mi of the line.
Limestone. Age: Middle Ordovician, 459 to 471 million years old. About 2 mi of the line.
Limestone. Age: Early Mississippian to Middle Mississippian, 331 to 359 million years old. About 2 mi of the line.
Limestone. Age: Carboniferous, 324 to 359 million years old. About 2 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 Prairie du Rocher reaches the Gulf of America by way of Prairie du Rocher Creek and the Mississippi: about 1,100 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Prairie du Rocher; river miles along the main stem, rounded.
Prairie du Rocher has a hot-summer humid continental climate. Summer afternoons average 89° in July; winter nights fall to about 24° in January. About 43 inches of rain fall in a normal year, with about 4 inches of snow.
On November 14 Prairie du Rocher normally reaches 56° and falls to 37°. The record high is 86°, in 1999; the record low 9°, in 1986. The most rain on this date, 3.40 in, fell in 1993.
Normals 1991–2020 and records since 1974 at Kaskaskia River Navigation Lock, 11 miles southeast. NOAA, through RCC-ACIS.
