The Algonac 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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4° on Nov. 16, 1933, the coldest reading for this week of the year since 1896. Next is 10° in 1908.
Algonac’s center stands about 590 ft above sea level. Within three miles the land runs from 570 ft to 660 ft, a difference of 90 ft: gently rolling country.
Under the town center the state geologic map shows Antrim Shale (black-shale), from the Late Devonian, 359 to 384 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 64×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Shale. Age: Late Devonian, 359 to 384 million years old. About 5 mi of the line.
Sandstone. Age: Late Devonian, 359 to 384 million years old. About 3 mi of the line.
Black-shale. Age: Late Devonian, 359 to 384 million years old. About 3 mi of the line.
Black-shale. Age: Devonian to Carboniferous, 324 to 422 million years old. About 1 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.
Algonac has a hot-summer humid continental climate. Summer afternoons average 82° in July; winter nights fall to about 18° in January. A normal year brings about 32 inches of snow; with the rain, that comes to about 35 inches of water.
On November 14 Algonac normally reaches 48° and falls to 33°. The record high is 70°, in 1909; the record low 11°, in 1933. The most rain on this date, 0.94 in, fell in 1957.
Normals 1991–2020 and records since 1896 at Mt. Clemens Ang Base, 15 miles west. NOAA, through RCC-ACIS.
