The Bethesda 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.
Bethesda’s center stands about 330 ft above sea level. Within three miles the land runs from 30 ft to 400 ft, a difference of 370 ft: rolling country. The highest named summit within 15 miles is Hunting Hill, about 520 ft, 9 miles northwest.
Under the town center the state geologic map shows Wissahickon Formation; Lower Pelitic Schist (biotite-schist), from the Proterozoic, 542 to 2,500 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 36×. 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 8 mi of the line.
Biotite-schist. Age: Proterozoic, 542 to 2,500 million years old. About 4 mi of the line.
Tonalite. Age: Proterozoic to Paleozoic, 252 to 2,500 million years old. About 3 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Gravel, sand. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Biotite-gneiss. Age: Middle Ordovician to Late Ordovician, 456 to 464 million years old. About 0.9 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 Bethesda reaches Chesapeake Bay and the Atlantic Ocean by way of Booze Creek, 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 Bethesda; river miles along the main stem, rounded.
Bethesda 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 Bethesda 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, 10 miles south-southeast, 320 ft lower). NOAA, through RCC-ACIS.
