The Unionville 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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3.09 inches of rain fell in two days, the most for this week of the year since records began in 1946. The next wettest, 2.22 inches, fell in 2009.
Unionville’s center stands about 480 ft above sea level. Within three miles the land runs from 350 ft to 540 ft, a difference of 190 ft: gently rolling country. The highest named summit within 15 miles is Thorofare Mountain, about 1,250 ft, 15 miles northwest.
Under the town center the state geologic map shows Metagraywacke, Quartzose Schist, and Melange (metagraywacke, mica-schist), from the Neoproterozoic to Cambrian, 487 to 1,000 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 26×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granodiorite. Age: Ordovician to Silurian, 422 to 487 million years old. About 5 mi of the line.
Metabasalt. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 4 mi of the line.
Metagraywacke, mica-schist. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 3 mi of the line.
Basalt. Age: Early Jurassic, 175 to 202 million years old. About 3 mi of the line.
Melange. Age: Neoproterozoic to Ordovician, 445 to 1,000 million years old. About 2 mi of the line.
Monzonite. Age: Ordovician, 445 to 487 million years old. About 2 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 Unionville reaches Chesapeake Bay and the Atlantic Ocean by way of Berry Run, Pamunkey Creek, the North Anna, the Pamunkey and the York: about 190 river miles.
90 miles of the trip are on the Pamunkey.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Unionville; river miles along the main stem, rounded.
Unionville has a humid subtropical climate. Summer afternoons average 87° in July; winter nights fall to about 25° in January. A normal year brings about 16 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 Unionville normally reaches 58° and falls to 37°. The record high is 77°, in 1994; the record low 15°, in 1986. The most rain on this date, 1.28 in, fell in 1972.
Normals 1991–2020 and records since 1946 at Piedmont Research Station, 8 miles west-southwest. NOAA, through RCC-ACIS.
