The Rockville 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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80° on Nov. 16, 1993, the hottest reading for this week of the year since 1941. Next is 78° in 1985.
Rockville’s center stands about 460 ft above sea level. Within three miles the land runs from 280 ft to 510 ft, a difference of 230 ft: rolling country. The highest named summit within 15 miles is Annapolis Rock, about 620 ft, 14 miles north.
Under the town center the state geologic map shows Wissahickon Formation (Undivided) (muscovite-schist), from the Proterozoic, 542 to 2,500 million years old.
The section below crosses 4 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 34×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Muscovite-schist. Age: Proterozoic, 542 to 2,500 million years old. About 19 mi of the line.
Melange. Age: Cambrian, 487 to 542 million years old. About 4 mi of the line.
Serpentinite. Age: Proterozoic to Paleozoic, 252 to 2,500 million years old. About 0.5 mi of the line.
Tonalite. Age: Proterozoic to Paleozoic, 252 to 2,500 million years old. About 0.3 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
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 Rockville reaches Chesapeake Bay and the Atlantic Ocean by way of Cabin John Creek and the Potomac: about 130 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Rockville; river miles along the main stem, rounded.
Rockville 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 Rockville normally reaches 57° and falls to 37°. The record high is 77°, in 1955; the record low 18°, in 1986. The most rain on this date, 0.98 in, fell in 1972.
Normals 1991–2020 and records since 1941 at Beltsville, 13 miles east-southeast, 320 ft lower. NOAA, through RCC-ACIS.
