The St. Clair 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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74° on Nov. 11, 2020, the hottest reading for this week of the year since 1964. Next is 70° in 1964.
St. Clair’s center stands about 2,300 ft above sea level. Within three miles the land runs from 1,080 ft to 2,710 ft, a difference of 1,630 ft: steep hill country. The highest named summit within 15 miles is Pea Vine Hill, about 2,940 ft, 13 miles south-southwest.
Under the town center the state geologic map shows Pottsville Formation (sandstone, conglomerate), 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 11×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone. Age: Carboniferous, 324 to 359 million years old. About 10 mi of the line.
Shale. Age: Carboniferous, 299 to 324 million years old. About 7 mi of the line.
Sandstone, conglomerate. Age: Carboniferous, 299 to 324 million years old. About 4 mi of the line.
Sandstone. Age: Carboniferous, 299 to 324 million years old. About 2 mi of the line.
Sandstone, siltstone, shale. Age: Devonian to Carboniferous, 324 to 422 million years old. About 1 mi of the line.
Shale, siltstone, sandstone. Age: Carboniferous, 324 to 359 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 St. Clair reaches the Gulf of America by way of Powdermill Run, the Conemaugh, the Kiskiminetas, the Allegheny, the Ohio and the Mississippi: about 2,040 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 St. Clair; river miles along the main stem, rounded.
St. Clair has a warm-summer humid continental climate. Summer afternoons average 79° in July; winter nights fall to about 16° in January. A normal year brings about 80 inches of snow; with the rain, that comes to about 49 inches of water.
On November 14 St. Clair normally reaches 48° and falls to 29°. The record high is 69°, in 1994; the record low 5°, in 1986. The most rain on this date, 0.74 in, fell in 1993.
Normals 1991–2020 and records since 1964 at Ebensburg Sewage Plant, 18 miles east-northeast, 360 ft lower. NOAA, through RCC-ACIS.
