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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72° on Nov. 11, 2020, the hottest reading for this week of the year since 1948. Next is 71° in 1989.
Groton’s center stands about 640 ft above sea level. Within three miles the land runs from 580 ft to 2,160 ft, a difference of 1,580 ft: steep hill country. The highest named summit within 15 miles is Smarts Mountain, about 3,220 ft, 13 miles northwest.
Under the town center the state geologic map shows Kinsman Granodiorite, from the Early Devonian, 394 to 422 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 8×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granite. Age: Late Devonian, 359 to 384 million years old. About 9 mi of the line.
Granodiorite. Age: Early Devonian, 394 to 422 million years old. About 7 mi of the line.
Metaclastic. Age: Early Devonian, 394 to 422 million years old. About 6 mi of the line.
Metasedimentary. 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.
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 the Cockermouth, the Newfound, the Pemigewasset and the Merrimack: about 140 river miles.
Lake on the way: Newfound Lake.
120 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 warm-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 9° in January. About 46 inches of rain fall in a normal year.
On November 14 Groton normally reaches 46° and falls to 27°. The record high is 65°, in 2010; the record low 9°, in 2019. The most rain on this date, 0.90 in, fell in 1975.
Normals 1991–2020 and records since 1948 at Franklin Falls Dam, 18 miles south-southeast, 190 ft lower. NOAA, through RCC-ACIS.
