The Fairfax 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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76° on Nov. 12, 2014, the hottest reading for this week of the year since 1925. Next is 75° in 2020.
Fairfax’s center stands about 430 ft above sea level. Within three miles the land runs from 300 ft to 490 ft, a difference of 190 ft: gently rolling country.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 43×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Metasiltstone. Age: Cambrian to Ordovician, 445 to 542 million years old. About 11 mi of the line.
Melange. Age: Cambrian, 487 to 542 million years old. About 5 mi of the line.
Schist. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 5 mi of the line.
Gravel, sand. Age: Tertiary, 2.6 to 66 million years old. About 1 mi of the line.
Phyllite. Age: Cambrian to Ordovician, 445 to 542 million years old. About 0.8 mi of the line.
Metasandstone. Age: Cambrian, 487 to 542 million years old. About 0.6 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 Fairfax reaches Chesapeake Bay and the Atlantic Ocean by way of Accotink Creek and the Potomac: about 120 river miles.
95 miles of the trip are on the Potomac.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Fairfax; river miles along the main stem, rounded.
Fairfax has a humid subtropical climate. Summer afternoons average 84° in July; winter nights fall to about 23° in January. A normal year brings about 18 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 Fairfax normally reaches 56° and falls to 35°. The record high is 65°, in 2005; the record low 22°, in 2019. The most rain on this date, 1.53 in, fell in 1972.
Normals 1991–2020 and records since 1925 at Vienna, 3 miles north-northeast. NOAA, through RCC-ACIS.
