The Thornapple 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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−3° on Nov. 17, 1959, the coldest reading for this week of the year since 1929. Next is −3° in 1986.
Thornapple’s center stands about 1,080 ft above sea level. Within three miles the land runs from 1,070 ft to 1,180 ft, a difference of 110 ft: gently rolling country. The highest named summit within 15 miles is Bald Hill, about 1,730 ft, 11 miles west-northwest.
Under the town center the state geologic map shows Cambrian, undivided (sandstone), from the Cambrian, 487 to 542 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 37×. 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 542 million years old. About 16 mi of the line.
Basalt, basaltic-andesite. Age: Paleoproterozoic, 1.6 to 2.5 billion years old. About 3 mi of the line.
Metavolcanic. Age: Paleoproterozoic, 1.6 to 2.5 billion years old. About 2 mi of the line.
Metavolcanic. Age: Paleoproterozoic, 1.6 to 2.5 billion years old. About 2 mi of the line.
Quartzite. Age: Paleoproterozoic, 1.6 to 2.5 billion 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.
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 Thornapple reaches the Gulf of America by way of Buff Creek, the Chippewa and the Mississippi: about 1,880 river miles.
Lakes on the way: Lake Wissota and Holcombe Flowage.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Thornapple; river miles along the main stem, rounded.
Thornapple has a warm-summer humid continental climate. Summer afternoons average 80° in July; winter nights fall to about 2° in January. About 33 inches of rain fall in a normal year.
On November 14 Thornapple normally reaches 40° and falls to 24°. The record high is 65°, in 1990; the record low 3°, in 1959. The most rain on this date, 0.75 in, fell in 2005.
Normals 1991–2020 and records since 1929 at Holcombe, 14 miles south-southeast. NOAA, through RCC-ACIS.
