The Mackinac Island 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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78° on Nov. 11, 2022, the hottest reading for this week of the year since 1891. Next is 71° in 1915.
Mackinac Island’s center stands about 610 ft above sea level. Within three miles the land runs from 570 ft to 810 ft, a difference of 240 ft: rolling country.
Under the town center the state geologic map shows Mackinac Breccia (limestone, sedimentary-breccia), 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 57×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Limestone. Age: Early Devonian, 394 to 422 million years old. About 2 mi of the line.
Limestone, sedimentary-breccia. Age: Early Devonian, 394 to 422 million years old. About 2 mi of the line.
Dolostone. Age: Middle Devonian, 384 to 394 million years old. About 2 mi of the line.
Shale. Age: Silurian, 422 to 428 million years old. About 0.9 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.
Mackinac Island has a warm-summer humid continental climate. Summer afternoons average 77° in July; winter nights fall to about 10° in February. A normal year brings about 88 inches of snow; with the rain, that comes to about 32 inches of water.
On November 14 Mackinac Island normally reaches 44° and falls to 30°. The record high is 64°, in 1999; the record low 11°, in 1933. The most rain on this date, 0.69 in, fell in 1957.
Normals 1991–2020 and records since 1891 at Cheboygan, 15 miles south-southeast. NOAA, through RCC-ACIS.
