The Swans 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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Swans Island’s center stands about 80 ft above sea level. Within three miles the land runs from 0 ft to 210 ft, a difference of 210 ft: rolling country. Open water lies within three miles. The highest named summit within 15 miles is Western Mountain, about 1,080 ft, 12 miles north-northeast.
Under the town center the state geologic map shows Devonian granite, from the Devonian, 359 to 422 million years old.
The section below crosses 3 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.
Granite. Age: Devonian, 359 to 422 million years old. About 5 mi of the line.
Felsic-volcanic, mafic-volcanic. Age: Middle Cambrian, 499 to 507 million years old. About 4 mi of the line.
Gabbro, diorite, ultramafic. Age: Devonian, 359 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.
