The Savanna 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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−2° on Nov. 12, 2019, the coldest reading for this week of the year since 1895. Next is −1° in 1898.
Savanna’s center stands about 600 ft above sea level. Within three miles the land runs from 570 ft to 870 ft, a difference of 300 ft: rolling country. The highest named summit within 15 miles is Heer Hill, about 940 ft, 9 miles north.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 50×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Dolostone, limestone. Age: Silurian, 422 to 445 million years old. About 9 mi of the line.
Dolostone. Age: Late Ordovician to Silurian, 434 to 447 million years old. About 6 mi of the line.
Shale, dolostone. Age: Late Ordovician, 447 to 454 million years old. About 4 mi of the line.
Shale, limestone. Age: Late Ordovician, 445 to 454 million years old. About 3 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million years old. About 2 mi of the line.
Dolostone, limestone. Age: Late Ordovician, 447 to 459 million 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.
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 Savanna reaches the Gulf of America by way of the Plum and the Mississippi: about 1,520 river miles.
Lake on the way: Spring Lake.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Savanna; river miles along the main stem, rounded.
Savanna has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 11° in January. A normal year brings about 33 inches of snow; with the rain, that comes to about 40 inches of water.
On November 14 Savanna normally reaches 49° and falls to 28°. The record high is 73°, in 1999; the record low 3°, in 1986. The most rain on this date, 1.30 in, fell in 1899.
Normals 1991–2020 and records since 1895 at Mount Carroll, 9 miles east, 110 ft higher. NOAA, through RCC-ACIS.
