The Grayhawk 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.
Grayhawk’s center stands about 770 ft above sea level. Within three miles the land runs from 470 ft to 1,010 ft, a difference of 540 ft: hilly country. The highest named summit within 15 miles is Wiggins Hill, about 1,170 ft, 12 miles west-southwest.
Under the town center the state geologic map shows Roubidoux Formation (sandstone, chert), from the Early Ordovician, 471 to 487 million years old.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 28×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone. Age: Cambrian, 487 to 497 million years old. About 8 mi of the line.
Dolostone. Age: Early Ordovician, 471 to 487 million years old. About 3 mi of the line.
Dolostone, shale, siltstone. Age: Cambrian, 487 to 497 million years old. About 2 mi of the line.
Sandstone, chert. Age: Early Ordovician, 471 to 487 million years old. About 2 mi of the line.
Dolostone, sandstone, limestone. Age: Early Ordovician to Middle Ordovician, 459 to 487 million years old. About 2 mi of the line.
Clay, silt, sand. Age: Holocene, less than 12,000 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. 7 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 Grayhawk reaches the Gulf of America by way of Establishment Creek and the Mississippi: about 1,120 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grayhawk; river miles along the main stem, rounded.
Grayhawk 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 Grayhawk 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, 17 miles east-northeast, 380 ft lower. NOAA, through RCC-ACIS.
