The Chillum 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.
Chillum’s center stands about 160 ft above sea level. Within three miles the land runs from 30 ft to 350 ft, a difference of 320 ft: rolling country. The highest named summit within 15 miles is Hunting Hill, about 520 ft, 14 miles 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 5 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.
Sand. Age: Cretaceous, 66 to 145 million years old. About 8 mi of the line.
Biotite-schist. Age: Proterozoic, 542 to 2,500 million years old. About 6 mi of the line.
Muscovite-gneiss. Age: Proterozoic, 542 to 2,500 million years old. About 4 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 4 mi of the line.
Gravel, sand. Age: Pleistocene, less than 2.6 million years old. About 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 Chillum reaches Chesapeake Bay and the Atlantic Ocean by way of Sligo Creek, 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 Chillum; river miles along the main stem, rounded.
Chillum 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 Chillum 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, 8 miles south-southwest, 150 ft lower). NOAA, through RCC-ACIS.
