The Johnston 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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4.24 inches of rain fell in two days, the most for this week of the year since records began in 1902. The next wettest, 3.90 inches, fell in 1940.
Johnston’s center stands about 660 ft above sea level. Within three miles the land runs from 510 ft to 680 ft, a difference of 170 ft: gently rolling country.
Under the town center the state geologic map shows Huber/Lisbon/Barnwell Formations, undivided (clay, sand), from the Eocene, 34 to 56 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 56×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Metasiltstone, metasandstone. Age: Middle Cambrian, 497 to 521 million years old. About 9 mi of the line.
Clay, sand. Age: Eocene, 34 to 56 million years old. About 7 mi of the line.
Paragneiss. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 3 mi of the line.
Granite. Age: Carboniferous to Permian, 252 to 359 million years old. About 2 mi of the line.
Sand. Age: Cretaceous, 66 to 145 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.
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 Johnston reaches the Atlantic Ocean by way of Little Turkey Creek, Turkey Creek, Stevens Creek and the Savannah: about 270 river miles.
200 miles of the trip are on the Savannah.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Johnston; river miles along the main stem, rounded.
Johnston has a humid subtropical climate. Summer afternoons average 93° in July; winter nights fall to about 32° in January. About 47 inches of rain fall in a normal year.
On November 14 Johnston normally reaches 64° and falls to 39°. The record high is 86°, in 1931; the record low 21°, in 2013. The most rain on this date, 2.25 in, fell in 1997.
Normals 1991–2020 and records since 1902 at Saluda, 11 miles north, 180 ft lower. NOAA, through RCC-ACIS.
