The Grantham 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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73° on Nov. 11, 2020, the hottest reading for this week of the year since 1928. Next is 70° in 1993.
Grantham’s center stands about 990 ft above sea level. Within three miles the land runs from 910 ft to 1,960 ft, a difference of 1,050 ft: steep hill country. The highest named summit within 15 miles is Croydon Peak, about 2,740 ft, 4 miles west.
Under the town center the state geologic map shows Bethlehem Granodiorite, from the Early Devonian, 394 to 422 million years old.
The section below crosses 13 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 11×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granodiorite. Age: Early Devonian, 394 to 422 million years old. About 7 mi of the line.
Metavolcanic, metasedimentary. Age: Middle Ordovician to Late Ordovician, 445 to 471 million years old. About 3 mi of the line.
Granite. Age: Late Devonian, 359 to 384 million years old. About 3 mi of the line.
Granodiorite. Age: Early Devonian, 394 to 422 million years old. About 2 mi of the line.
Granite, granodiorite, trondhjemite. Age: Late Ordovician, 445 to 459 million years old. About 2 mi of the line.
Slate, phyllite. Age: Late Ordovician, 445 to 459 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. 7 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 Grantham reaches Long Island Sound and the Atlantic Ocean by way of Sawyer Brook, the North Branch Sugar, the Sugar and the Connecticut: about 230 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grantham; river miles along the main stem, rounded.
Grantham has a warm-summer humid continental climate. Summer afternoons average 80° in July; winter nights fall to about 9° in January. A normal year brings about 66 inches of snow; with the rain, that comes to about 42 inches of water.
On November 14 Grantham normally reaches 46° and falls to 27°. The record high is 62°, in 2010; the record low 8°, in 2019. The most rain on this date, 2.64 in, fell in 1937.
Normals 1991–2020 and records since 1928 at Newport, 8 miles south-southwest, 220 ft lower. NOAA, through RCC-ACIS.
