The Cohasset 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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−20° on Nov. 16, 1933, the coldest reading for this week of the year since 1887. Next is −12° in 1894.
Cohasset’s center stands about 1,280 ft above sea level. Within three miles the land runs from 1,270 ft to 1,380 ft, a difference of 110 ft: gently rolling country. The highest named summit within 15 miles is Big Thunder Peak, about 1,820 ft, 10 miles south-southwest.
Under the town center the state geologic map shows Foliated to gneissic tonalite, granodiorite, and diorite (tonalite, granodiorite, diorite), from the Neoarchean, 2.5 to 2.8 billion years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 50×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Tonalite, granodiorite, diorite. Age: Neoarchean, 2.5 to 2.8 billion years old. About 14 mi of the line.
Metabasalt, greenstone. Age: Neoarchean, 2.5 to 2.8 billion years old. About 5 mi of the line.
Conglomerate, lignite, sandstone. Age: Late Cretaceous, 94 to 100 million years old. About 3 mi of the line.
Slate, graywacke. Age: Paleoproterozoic, 1.6 to 2 billion years old. About 1 mi of the line.
Banded-iron-formation, sedimentary-breccia. Age: Paleoproterozoic, 1.8 to 2 billion years old. About 0.6 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 Cohasset reaches the Gulf of America by way of the Mississippi: about 2,160 river miles.
Lake on the way: Lake Pepin.
1,750 miles of the trip are on the Mississippi.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Cohasset; river miles along the main stem, rounded.
Cohasset has a warm-summer humid continental climate. Summer afternoons average 78° in July; winter nights fall to about −3° in January. About 28 inches of rain fall in a normal year.
On November 14 Cohasset normally reaches 37° and falls to 21°. The record high is 64°, in 1953; the record low −9°, in 1959. The most rain on this date, 0.71 in, fell in 1909.
Normals 1991–2020 and records since 1887 at Pokegama Dam, here. NOAA, through RCC-ACIS.
