The Groton 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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76° on Nov. 11, 2020, the hottest reading for this week of the year since 1885. Next is 75° in 1909.
Groton’s center stands about 310 ft above sea level. Within three miles the land runs from 190 ft to 450 ft, a difference of 260 ft: rolling country. The highest named summit within 15 miles is Brown Hill, about 1,230 ft, 14 miles west.
Under the town center the state geologic map shows Berwick Formation (metaclastic), from the Silurian, 422 to 445 million years old.
The section below crosses 14 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 25×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granofels, schist. Age: Neoproterozoic, 542 to 1,000 million years old. About 4 mi of the line.
Metasedimentary, muscovite-schist. Age: Neoproterozoic, 542 to 1,000 million years old. About 3 mi of the line.
Metaclastic. Age: Silurian, 422 to 445 million years old. About 3 mi of the line.
Granite, granodiorite. Age: Silurian, 428 to 445 million years old. About 3 mi of the line.
Granite, pegmatite. Age: Ordovician to Silurian, 422 to 487 million years old. About 2 mi of the line.
Schist, phyllite. Age: Early Devonian, 394 to 422 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 8 smaller units 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 Groton reaches the Atlantic Ocean by way of James Brook, the Nashua and the Merrimack: about 80 river miles.
55 miles of the trip are on the Merrimack.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Groton; river miles along the main stem, rounded.
Groton has a hot-summer humid continental climate. Summer afternoons average 85° in July; winter nights fall to about 16° in January. About 48 inches of rain fall in a normal year.
On November 14 Groton normally reaches 51° and falls to 31°. The record high is 70°, in 1959; the record low 12°, in 1905. The most rain on this date, 2.03 in, fell in 1895.
Normals 1991–2020 and records since 1885 at Lowell, 10 miles east, 200 ft lower. NOAA, through RCC-ACIS.
