The Orrtanna 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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14° on Nov. 14, 1986, the coldest reading for this week of the year since 1972. Next is 15° in 1996.
Orrtanna’s center stands about 680 ft above sea level. Within three miles the land runs from 550 ft to 1,430 ft, a difference of 880 ft: hilly country. The highest named summit within 15 miles is Quirauk Mountain, about 2,150 ft, 13 miles southwest.
Under the town center the state geologic map shows Diabase (basalt), from the Jurassic, 145 to 202 million years old.
The section below crosses 7 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.
Siltstone-mudstone, shale. Age: Triassic, 202 to 252 million years old. About 7 mi of the line.
Quartzite. Age: Cambrian, 487 to 542 million years old. About 5 mi of the line.
Basalt. Age: Jurassic, 145 to 202 million years old. About 3 mi of the line.
Shale. Age: Triassic, 202 to 252 million years old. About 3 mi of the line.
Age: Precambrian. About 3 mi of the line.
Quartzite. Age: Cambrian, 487 to 542 million years old. About 3 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 Orrtanna reaches Chesapeake Bay and the Atlantic Ocean by way of Little Marsh Creek, Marsh Creek, the Monocacy and the Potomac: about 230 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 Orrtanna; river miles along the main stem, rounded.
Orrtanna 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 27 inches of snow; with the rain, that comes to about 45 inches of water.
On November 14 Orrtanna normally reaches 54° and falls to 35°. The record high is 66°, in 1973; the record low 14°, in 1986. The most rain on this date, 1.28 in, fell in 1972.
Normals 1991–2020 and records since 1972 at Biglerville, 8 miles northeast. NOAA, through RCC-ACIS.
