The Potomac Mills 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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3.72 inches of rain fell in two days, the most for this week of the year since records began in 1945. The next wettest, 2.62 inches, fell in 2009.
Potomac Mills’s center stands about 220 ft above sea level. Within three miles the land runs from 0 ft to 360 ft, a difference of 360 ft: rolling country. The highest named summit within 15 miles is Signal Hill, about 420 ft, 11 miles northwest.
The section below crosses 10 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 45×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sand. Age: Cretaceous, 66 to 145 million years old. About 7 mi of the line.
Granite. Age: Cambrian to Ordovician, 445 to 542 million years old. About 6 mi of the line.
Melange. Age: Cambrian, 487 to 542 million years old. About 2 mi of the line.
Metasiltstone. Age: Cambrian to Ordovician, 445 to 542 million years old. About 2 mi of the line.
Sand, silt. Age: Tertiary, 2.6 to 66 million years old. About 1 mi of the line.
Sand, silt, peat. Age: Quaternary, less than 2.6 million years old. About 0.8 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 4 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 Potomac Mills reaches Chesapeake Bay and the Atlantic Ocean by way of Neabsco Creek and the Potomac: about 95 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Potomac Mills; river miles along the main stem, rounded.
Potomac Mills has a humid subtropical climate. Summer afternoons average 88° in July; winter nights fall to about 28° in January. A normal year brings about 12 inches of snow; with the rain, that comes to about 41 inches of water.
On November 14 Potomac Mills normally reaches 58° and falls to 40°. The record high is 80°, in 1985; the record low 23°, in 1986. The most rain on this date, 1.60 in, fell in 1972.
Normals 1991–2020 and records since 1945 at Quantico Mcas, 10 miles south, 210 ft lower. NOAA, through RCC-ACIS.
