The Annandale 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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83° on Nov. 15, 1993, the hottest reading for this week of the year since 1871. Next is 80° in 1879.
Annandale’s center stands about 360 ft above sea level. Within three miles the land runs from 190 ft to 400 ft, a difference of 210 ft: rolling country. The highest named summit within 15 miles is Gantt Hill, about 510 ft, 7 miles north-northwest.
Under the town center the state geologic map shows Indian Run Formation (melange), from the Cambrian, 487 to 542 million years old.
The section below crosses 12 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 39×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Schist. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 6 mi of the line.
Sand. Age: Cretaceous, 66 to 145 million years old. About 5 mi of the line.
Tonalite. Age: Cambrian to Ordovician, 445 to 542 million years old. About 2 mi of the line.
Gravel, sand. Age: Pliocene, 2.6 to 5.3 million years old. About 2 mi of the line.
Fine-detrital, coarse-detrital. Age: Quaternary, less than 2.6 million years old. About 1 mi of the line.
Melange. Age: Cambrian, 487 to 542 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. 6 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 Annandale reaches Chesapeake Bay and the Atlantic Ocean by way of Accotink Creek and the Potomac: about 110 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 Annandale; river miles along the main stem, rounded.
Annandale has a humid subtropical climate. Summer afternoons average 90° in July; winter nights fall to about 30° in January. A normal year brings about 14 inches of snow; with the rain, that comes to about 42 inches of water.
On November 14 Annandale normally reaches 59° and falls to 42°. The record high is 77°, in 1985; the record low 19°, in 1920. The most rain on this date, 1.56 in, fell in 1972.
Normals 1991–2020 and records since 1871 from the Washington Area threaded record (Washington Reagan National Airport, 9 miles east, 350 ft lower). NOAA, through RCC-ACIS.
