The Jonestown 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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75° on Nov. 15, 1993, the hottest reading for this week of the year since 1948. Next is 74° in 1973.
Jonestown’s center stands about 450 ft above sea level. Within three miles the land runs from 410 ft to 650 ft, a difference of 240 ft: rolling country. The highest named summit within 15 miles is Big Lick Mountain, about 1,820 ft, 14 miles north-northwest.
Under the town center the state geologic map shows Hamburg sequence rocks (shale), from the Ordovician, 445 to 487 million years old.
The section below crosses 19 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 15×. 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 9 mi of the line.
Shale, siltstone, sandstone. Age: Carboniferous, 324 to 359 million years old. About 2 mi of the line.
Dolostone. Age: Cambrian, 487 to 542 million years old. About 2 mi of the line.
Siltstone, shale. Age: Late Devonian, 359 to 384 million years old. About 1 mi of the line.
Graywacke. Age: Ordovician, 445 to 487 million years old. About 1 mi of the line.
Limestone, dolostone. 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. 13 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 Jonestown reaches Chesapeake Bay and the Atlantic Ocean by way of Swatara Creek and the Susquehanna: about 100 river miles.
Lake on the way: Lake Aldred.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Jonestown; river miles along the main stem, rounded.
Jonestown has a hot-summer humid continental climate. Summer afternoons average 84° in July; winter nights fall to about 22° in January. A normal year brings about 24 inches of snow; with the rain, that comes to about 46 inches of water.
On November 14 Jonestown normally reaches 53° and falls to 34°. The record high is 72°, in 1989; the record low 17°, in 1986. The most rain on this date, 1.69 in, fell in 1972.
Normals 1991–2020 and records since 1948 at Lebanon 2 W, 5 miles south. NOAA, through RCC-ACIS.
