The Mercersburg 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.
Mostly cloudy
Mostly cloudy
Mostly sunny
Sunny
Sunny
Mostly sunny
Mostly sunny
1° on Nov. 16, 1908, the coldest reading for this week of the year since 1899. Next is 9° in 1933.
Mercersburg’s center stands about 560 ft above sea level. Within three miles the land runs from 510 ft to 1,530 ft, a difference of 1,020 ft: steep hill country. The highest named summit within 15 miles is Big Mountain, about 2,460 ft, 8 miles north-northwest.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 10×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Graywacke, shale. Age: Ordovician, 445 to 487 million years old. About 4 mi of the line.
Shale. Age: Ordovician, 445 to 487 million years old. About 4 mi of the line.
Dolostone. Age: Ordovician, 445 to 487 million years old. About 3 mi of the line.
Limestone. 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.
Quartzite. Age: Silurian, 422 to 445 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. 7 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 Mercersburg reaches Chesapeake Bay and the Atlantic Ocean by way of Johnston Run, West Branch Conococheague Creek, Conococheague Creek and the Potomac: about 250 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 Mercersburg; river miles along the main stem, rounded.
Mercersburg 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 Mercersburg 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, 13 miles southeast, 130 ft higher). NOAA, through RCC-ACIS.
