The Mount Joy 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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77° on Nov. 15, 1973, the hottest reading for this week of the year since 1956. Next is 76° in 2020.
Mount Joy’s center stands about 550 ft above sea level. Within three miles the land runs from 400 ft to 610 ft, a difference of 210 ft: rolling country. The highest named summit within 15 miles is Piney Mountain, about 1,730 ft, 15 miles west-southwest.
Under the town center the state geologic map shows Gettysburg Formation (siltstone-mudstone, shale), from the Triassic, 202 to 252 million years old.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 21×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Siltstone-mudstone, shale. Age: Triassic, 202 to 252 million years old. About 8 mi of the line.
Arkose. Age: Triassic, 202 to 252 million years old. About 4 mi of the line.
Quartzite. Age: Cambrian, 487 to 542 million years old. About 4 mi of the line.
Basalt. Age: Jurassic, 145 to 202 million years old. About 3 mi of the line.
Limestone. Age: Cambrian to Ordovician, 445 to 542 million years old. About 3 mi of the line.
Quartzite. Age: Cambrian, 487 to 542 million years old. About 1 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 3 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 Mount Joy reaches Chesapeake Bay and the Atlantic Ocean by way of Littles Run, Rock Creek, the Monocacy and the Potomac: about 220 river miles.
160 miles of the trip are on the Potomac.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Mount Joy; river miles along the main stem, rounded.
Mount Joy has a hot-summer humid continental climate. Summer afternoons average 86° in July; winter nights fall to about 22° in January. A normal year brings about 28 inches of snow; with the rain, that comes to about 47 inches of water.
On November 14 Mount Joy normally reaches 55° and falls to 34°. The record high is 72°, in 1989; the record low 15°, in 1986. The most rain on this date, 2.25 in, fell in 1972.
Normals 1991–2020 and records since 1956 at Emmitsburg 2 SE, 8 miles southwest, 150 ft lower. NOAA, through RCC-ACIS.
