The Upper Grand Lagoon 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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Upper Grand Lagoon’s center stands barely above sea level. Within three miles the land runs from 0 ft to 40 ft, a difference of 40 ft: nearly flat ground. Open water lies within three miles.
The section below crosses 2 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, clay. Age: Pleistocene to Holocene, less than 2.6 million years old. About 11 mi of the line.
Sand. Age: Holocene, less than 12,000 years old. About 0.4 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 Upper Grand Lagoon runs straight into St. Andrew Bay and the Gulf of America.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Upper Grand Lagoon; river miles along the main stem, rounded.
