The Grottoes 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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80° on Nov. 12, 1931, the hottest reading for this week of the year since 1893. Next is 78° in 1924.
Grottoes’s center stands about 1,110 ft above sea level. Within three miles the land runs from 1,050 ft to 1,480 ft, a difference of 430 ft: hilly country. The highest named summit within 15 miles is Big Flat Mountain, about 3,390 ft, 9 miles east.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 8×. 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 5 mi of the line.
Quartzite, conglomerate, sandstone. Age: Cambrian, 487 to 542 million years old. About 4 mi of the line.
Dolostone, limestone. Age: Ordovician, 445 to 487 million years old. About 3 mi of the line.
Age: Mesoproterozoic, 1 to 1.6 billion years old. About 3 mi of the line.
Metabasalt. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 2 mi of the line.
Dolostone, limestone. Age: Cambrian, 487 to 542 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 3 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 Grottoes reaches Chesapeake Bay and the Atlantic Ocean by way of Miller Run, the South Fork Shenandoah, the Shenandoah and the Potomac: about 330 river miles.
180 miles of the trip are on the Potomac.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grottoes; river miles along the main stem, rounded.
Grottoes has a humid subtropical climate. Summer afternoons average 86° in July; winter nights fall to about 23° in January. A normal year brings about 19 inches of snow; with the rain, that comes to about 39 inches of water.
On November 14 Grottoes normally reaches 56° and falls to 33°. The record high is 78°, in 1924; the record low 9°, in 1920. The most rain on this date, 1.00 in, fell in 1908.
Normals 1991–2020 and records since 1893 at Dale Enterprise, 14 miles north-northwest, 250 ft higher. NOAA, through RCC-ACIS.
