The Gwynn 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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Gwynn’s center stands about 30 ft above sea level. Within three miles the land runs from 0 ft to 80 ft, a difference of 80 ft: gently rolling country. Open water lies within three miles.
Under the town center the state geologic map shows Tabb Formation: Lynnhaven and Poquoson Members (sand, silt), from the Quaternary, less than 2.6 million 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 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.
Sand, silt. Age: Quaternary, less than 2.6 million years old. About 8 mi of the line.
Sand. Age: Quaternary, less than 2.6 million years old. About 1 mi of the line.
Fine-detrital, coarse-detrital. Age: Tertiary to Quaternary, less than 66 million years old. About 1 mi of the line.
Sand. Age: Holocene, less than 12,000 years old. About 0.3 mi of the line.
Sand. Age: Tertiary, 2.6 to 66 million years old. About 0.1 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.
Rain that falls on Gwynn runs straight into Chesapeake Bay and the Atlantic Ocean.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Gwynn; river miles along the main stem, rounded.
