The Dahlgren 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.
Dahlgren’s center stands about 20 ft above sea level. Within three miles the land runs from 0 ft to 140 ft, a difference of 140 ft: gently rolling country. Open water lies within three miles. The highest named summit within 15 miles is Cedar Hill, about 230 ft, 15 miles south-southeast.
Under the town center the state geologic map shows Tabb Formation; Sedgefield Member (sand), from the Quaternary, less than 2.6 million years old.
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 64×. 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: Tertiary, 2.6 to 66 million years old. About 4 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Sand. Age: Quaternary, less than 2.6 million years old. About 3 mi of the line.
Sand, silt. Age: Tertiary, 2.6 to 66 million years old. About 2 mi of the line.
Gravel. Age: Tertiary, 2.6 to 66 million years old. About 2 mi of the line.
Fine-detrital, coarse-detrital. Age: Tertiary to Quaternary, less than 66 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 Dahlgren reaches Chesapeake Bay and the Atlantic Ocean by way of Williams Creek, Upper Machodoc Creek and the Potomac: about 50 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Dahlgren; river miles along the main stem, rounded.
Dahlgren 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 Dahlgren 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, 18 miles northwest. NOAA, through RCC-ACIS.
