The St. Thomas 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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1° on Nov. 16, 1908, the coldest reading for this week of the year since 1899. Next is 9° in 1933.
St. Thomas’s center stands about 710 ft above sea level. Within three miles the land runs from 550 ft to 1,820 ft, a difference of 1,270 ft: steep hill country. The highest named summit within 15 miles is Big Mountain, about 2,460 ft, 7 miles west-northwest.
The section below crosses 15 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 11×. 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: Ordovician, 445 to 487 million years old. About 8 mi of the line.
Limestone. Age: Ordovician, 445 to 487 million years old. About 3 mi of the line.
Quartzite. Age: Silurian, 422 to 445 million years old. About 3 mi of the line.
Graywacke. Age: Ordovician, 445 to 487 million years old. About 2 mi of the line.
Shale. Age: Ordovician, 445 to 487 million years old. About 2 mi of the line.
Limestone. Age: Ordovician, 445 to 487 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. 9 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 St. Thomas reaches Chesapeake Bay and the Atlantic Ocean by way of Campbell Run, Back Creek, Conococheague Creek and the Potomac: about 260 river miles.
210 miles of the trip are on the Potomac.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of St. Thomas; river miles along the main stem, rounded.
St. Thomas has a humid subtropical climate. Summer afternoons average 87° in July; winter nights fall to about 25° in January. About 36 inches of rain fall in a normal year.
On November 14 St. Thomas normally reaches 55° and falls to 38°. The record high is 75°, in 1989; the record low 10°, in 1920. The most rain on this date, 1.91 in, fell in 1995.
Normals 1991–2020 and records since 1899 from the Hagerstown Area threaded record (Hagerstown Regional Airport, 16 miles south-southeast). NOAA, through RCC-ACIS.
