The Adelphi 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.
Adelphi’s center stands about 180 ft above sea level. Within three miles the land runs from 50 ft to 390 ft, a difference of 340 ft: rolling country. The highest named summit within 15 miles is Hunting Hill, about 520 ft, 13 miles west-northwest.
Under the town center the state geologic map shows Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation (sand), from the Cretaceous, 66 to 145 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 35×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Biotite-schist. Age: Proterozoic, 542 to 2,500 million years old. About 8 mi of the line.
Sand. Age: Cretaceous, 66 to 145 million years old. About 7 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Muscovite-gneiss. Age: Proterozoic, 542 to 2,500 million years old. About 3 mi of the line.
Sand. Age: Eocene, 34 to 56 million years old. About 1 mi of the line.
Gravel, sand. Age: Pleistocene, less than 2.6 million years old. About 0.5 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 Adelphi reaches Chesapeake Bay and the Atlantic Ocean by way of the Northwest Branch Anacostia, the Anacostia and the Potomac: about 120 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Adelphi; river miles along the main stem, rounded.
Adelphi 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 Adelphi 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, 3 miles northeast. NOAA, through RCC-ACIS.
