The Joppatowne 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. 15, 1993, the hottest reading for this week of the year since 1919. Next is 77° in 1955.
Joppatowne’s center stands about 60 ft above sea level. Within three miles the land runs from 0 ft to 270 ft, a difference of 270 ft: rolling country. Open water lies within three miles. The highest named summit within 15 miles is Schoolhouse Hill, about 380 ft, 15 miles north-northeast.
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 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 33×. 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 4 mi of the line.
Gabbro. Age: Proterozoic to Paleozoic, 252 to 2,500 million years old. About 4 mi of the line.
Biotite-schist. Age: Proterozoic, 542 to 2,500 million years old. About 4 mi of the line.
Gneiss, quartz-diorite, granodiorite. Age: Neoproterozoic to Middle Cambrian, 500 to 600 million years old. About 2 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 0.5 mi of the line.
Muscovite-gneiss. Age: Proterozoic, 542 to 2,500 million years old. About 0.4 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 Joppatowne reaches Chesapeake Bay and the Atlantic Ocean by way of Foster Branch and the Gunpowder: about 8 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Joppatowne; river miles along the main stem, rounded.
Joppatowne has a humid subtropical climate. Summer afternoons average 86° in July; winter nights fall to about 25° in January. About 47 inches of rain fall in a normal year.
On November 14 Joppatowne normally reaches 56° and falls to 37°. The record high is 77°, in 1955; the record low 21°, in 1986. The most rain on this date, 1.83 in, fell in 1972.
Normals 1991–2020 and records since 1919 at Aberdeen Phillips Field, 10 miles east-northeast. NOAA, through RCC-ACIS.
