The Decatur 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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12° on Nov. 15, 1969, the coldest reading for this week of the year since 1956. Next is 19° in 1974.
Decatur’s center stands about 770 ft above sea level. Within three miles the land runs from 680 ft to 1,100 ft, a difference of 420 ft: hilly country. The highest named summit within 15 miles is Lone Mountain, about 1,770 ft, 15 miles west.
Under the town center the state geologic map shows Chickamauga Group, includes Upper part of Chickamauga Group (Reedsville Shale, and Unnamed limestone unit) and Middle and Lower part of Chickamauga Group (Moccasin Formation, Bays Formation, Ottosee Shale, Holston Formation, Lenoir Limestone, Athens Shale, and Sevier Shale), from the Ordovician, 445 to 487 million years old.
The section below crosses 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 16×. 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. Age: Cambrian, 487 to 542 million years old. About 5 mi of the line.
Dolostone, limestone. Age: Cambrian to Ordovician, 445 to 542 million years old. About 4 mi of the line.
Limestone. Age: Ordovician, 445 to 487 million years old. About 4 mi of the line.
Dolostone, limestone. Age: Ordovician, 445 to 487 million years old. About 3 mi of the line.
Shale. Age: Cambrian, 487 to 542 million years old. About 2 mi of the line.
Dolostone. Age: Cambrian, 487 to 542 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. 5 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 Decatur reaches the Gulf of America by way of Decatur Branch, Decatur Creek, Goodfield Creek, the Tennessee, the Ohio and the Mississippi: about 1,540 river miles.
Lakes on the way: Guntersville Lake, White Lake (historical), Pickwick Lake and Cummings Lake.
970 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Decatur; river miles along the main stem, rounded.
Decatur has a humid subtropical climate. Summer afternoons average 88° in July; winter nights fall to about 28° in January. About 59 inches of rain fall in a normal year, with about 2 inches of snow.
On November 14 Decatur normally reaches 60° and falls to 37°. The record high is 75°, in 1973; the record low 19°, in 2019. The most rain on this date, 2.67 in, fell in 1957.
Normals 1991–2020 and records since 1956 at Dayton 2 SE, 12 miles west-southwest. NOAA, through RCC-ACIS.
