The Somerville 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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78° on Nov. 15, 1993, the hottest reading for this week of the year since 1872. Next is 76° in 1909.
Somerville’s center stands about 70 ft above sea level. Within three miles the land runs from 0 ft to 160 ft, a difference of 160 ft: gently rolling country. The highest named summit within 15 miles is Great Blue Hill, about 630 ft, 12 miles south.
Under the town center the state geologic map shows Cambridge Argillite, from the Neoproterozoic to Early Cambrian, 521 to 1,000 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 45×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Argillite. Age: Neoproterozoic to Early Cambrian, 521 to 1,000 million years old. About 11 mi of the line.
Metavolcanic. Age: Neoproterozoic, 542 to 1,000 million years old. About 4 mi of the line.
Diorite, gabbro. Age: Neoproterozoic, 542 to 1,000 million years old. About 3 mi of the line.
Granite, granodiorite. Age: Neoproterozoic, 615 to 645 million years old. About 0.8 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 Somerville reaches Boston Harbor and the Atlantic Ocean by way of the Mystic: about 3 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Somerville; river miles along the main stem, rounded.
Somerville has a hot-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 23° in January. A normal year brings about 49 inches of snow; with the rain, that comes to about 44 inches of water.
On November 14 Somerville normally reaches 52° and falls to 38°. The record high is 71°, in 1993; the record low 16°, in 1905. The most rain on this date, 1.49 in, fell in 2009.
Normals 1991–2020 and records since 1872 from the Boston Area threaded record (Boston Logan International Airport, 5 miles east-southeast). NOAA, through RCC-ACIS.
