The Dumbarton 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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5.05 inches of rain fell in two days, the most for this week of the year since records began in 1887. The next wettest, 2.76 inches, fell in 1902.
Dumbarton’s center stands about 210 ft above sea level. Within three miles the land runs from 130 ft to 320 ft, a difference of 190 ft: gently rolling country.
Under the town center the state geologic map shows Petersburg Granite, from the Carboniferous, 324 to 359 million years old.
The section below crosses 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 58×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Gravel, sand. Age: Pliocene, 2.6 to 5.3 million years old. About 8 mi of the line.
Granite. Age: Carboniferous, 324 to 359 million years old. About 5 mi of the line.
Fine-detrital, coarse-detrital. Age: Tertiary to Quaternary, less than 66 million years old. About 2 mi of the line.
Gravel, sand. Age: Tertiary, 2.6 to 66 million years old. About 2 mi of the line.
Sand, silt, clay. Age: Quaternary, less than 2.6 million years old. About 2 mi of the line.
Sand. Age: Tertiary, 2.6 to 66 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. 5 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 Dumbarton reaches Chesapeake Bay and the Atlantic Ocean by way of Upham Brook, the Chickahominy and the James: about 120 river miles.
65 miles of the trip are on the Chickahominy.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Dumbarton; river miles along the main stem, rounded.
Dumbarton has a humid subtropical climate. Summer afternoons average 90° in July; winter nights fall to about 29° in January. A normal year brings about 9 inches of snow; with the rain, that comes to about 46 inches of water.
On November 14 Dumbarton normally reaches 61° and falls to 39°. The record high is 81°, in 1993; the record low 18°, in 1976. The most rain on this date, 1.12 in, fell in 1940.
Normals 1991–2020 and records since 1887 from the Richmond Area threaded record (Richmond International Airport, 11 miles southeast). NOAA, through RCC-ACIS.
