The Twilight 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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13° on Nov. 13, 2019, the coldest reading for this week of the year since 1935. Next is 17° in 2017.
Twilight’s center stands about 1,060 ft above sea level. Within three miles the land runs from 740 ft to 1,300 ft, a difference of 560 ft: hilly country. The highest named summit within 15 miles is Fort Hill, about 1,590 ft, 11 miles east.
Under the town center the state geologic map shows Monongahela Group (limestone, shale, sandstone), from the Carboniferous, 299 to 324 million years old.
The section below crosses 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 25×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone, shale, sandstone. Age: Carboniferous, 299 to 324 million years old. About 10 mi of the line.
Sandstone, shale. Age: Carboniferous to Permian, 252 to 324 million years old. About 7 mi of the line.
Shale. Age: Carboniferous, 299 to 324 million years old. About 3 mi of the line.
Sandstone, shale. Age: Permian, 252 to 299 million years old. About 2 mi of the line.
Shale, clastic. Age: Carboniferous, 299 to 324 million years old. About 2 mi of the line.
Sandstone. Age: Carboniferous, 299 to 324 million years old. About 0.4 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
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 Twilight reaches the Gulf of America by way of South Branch Maple Creek, the Monongahela, the Ohio and the Mississippi: about 1,990 river miles.
970 miles of the trip are on the Ohio.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Twilight; river miles along the main stem, rounded.
Twilight has a hot-summer humid continental climate. Summer afternoons average 83° in July; winter nights fall to about 22° in January. About 41 inches of rain fall in a normal year.
On November 14 Twilight normally reaches 52° and falls to 36°. The record high is 70°, in 2011; the record low 18°, in 1942. The most rain on this date, 0.54 in, fell in 2011.
Normals 1991–2020 and records since 1935 at Pittsburgh Allegheny County Airport, 17 miles north, 180 ft higher. NOAA, through RCC-ACIS.
