The Orrstown 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 1910. Next is 75° in 1993.
Orrstown’s center stands about 680 ft above sea level. Within three miles the land runs from 570 ft to 770 ft, a difference of 200 ft: gently rolling country. The highest named summit within 15 miles is Clarks Knob, about 2,340 ft, 7 miles west.
The section below crosses 10 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 12×. 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 10 mi of the line.
Limestone. Age: Ordovician, 445 to 487 million years old. About 4 mi of the line.
Limestone, dolostone. Age: Cambrian, 487 to 542 million years old. About 3 mi of the line.
Quartzite. Age: Silurian, 422 to 445 million years old. About 2 mi of the line.
Limestone. Age: Cambrian, 487 to 542 million years old. About 2 mi of the line.
Sandstone. Age: Ordovician, 445 to 487 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. 4 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 Orrstown reaches Chesapeake Bay and the Atlantic Ocean by way of Muddy Run, Conodoguinet Creek and the Susquehanna: about 150 river miles.
Lake on the way: Lake Aldred.
75 miles of the trip are on Conodoguinet Creek.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Orrstown; river miles along the main stem, rounded.
Orrstown has a hot-summer humid continental climate. Summer afternoons average 88° in July; winter nights fall to about 22° in January. A normal year brings about 34 inches of snow; with the rain, that comes to about 42 inches of water.
On November 14 Orrstown normally reaches 54° and falls to 34°. The record high is 73°, in 1989; the record low 14°, in 1986. The most rain on this date, 1.88 in, fell in 1995.
Normals 1991–2020 and records since 1910 at Shippensburg, 5 miles east. NOAA, through RCC-ACIS.
