The Sylvan Hills 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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3.74 inches of rain fell in two days, the most for this week of the year since records began in 1967. The next wettest, 2.25 inches, fell in 1968.
Sylvan Hills’s center stands about 1,170 ft above sea level. Within three miles the land runs from 920 ft to 2,250 ft, a difference of 1,330 ft: steep hill country. The highest named summit within 15 miles is Blue Knob, about 3,140 ft, 15 miles southwest.
Under the town center the state geologic map shows Clinton Group (shale, sandstone), from the Silurian, 422 to 445 million years old.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 10×. 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, sandstone. Age: Silurian, 422 to 445 million years old. About 6 mi of the line.
Quartzite. Age: Silurian, 422 to 445 million years old. About 4 mi of the line.
Sandstone, shale. Age: Ordovician, 445 to 487 million years old. About 4 mi of the line.
Sandstone, siltstone, shale. Age: Late Devonian, 359 to 384 million years old. About 3 mi of the line.
Siltstone, shale. Age: Late Devonian, 359 to 384 million years old. About 1 mi of the line.
Sandstone. Age: Late Devonian, 359 to 384 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. 7 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 Sylvan Hills reaches Chesapeake Bay and the Atlantic Ocean by way of Brush Run, the Frankstown Branch Juniata, the Juniata and the Susquehanna: about 230 river miles.
Lake on the way: Lake Aldred.
100 miles of the trip are on the Juniata.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Sylvan Hills; river miles along the main stem, rounded.
Sylvan Hills has a warm-summer humid continental climate. Summer afternoons average 81° in July; winter nights fall to about 19° in January. A normal year brings about 38 inches of snow; with the rain, that comes to about 45 inches of water.
On November 14 Sylvan Hills normally reaches 49° and falls to 33°. The record high is 70°, in 2011; the record low 11°, in 1986. The most rain on this date, 1.18 in, fell in 1972.
Normals 1991–2020 and records since 1967 at Altoona 3 W, 5 miles northwest, 150 ft higher. NOAA, through RCC-ACIS.
