The Opal 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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Opal’s center stands about 450 ft above sea level. Within three miles the land runs from 310 ft to 540 ft, a difference of 230 ft: rolling country. The highest named summit within 15 miles is Wildcat Mountain, about 1,390 ft, 12 miles north.
The section below crosses 8 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 22×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Metabasalt. Age: Neoproterozoic to Cambrian, 487 to 1,000 million years old. About 11 mi of the line.
Shale, siltstone. Age: Triassic, 202 to 252 million years old. About 5 mi of the line.
Basalt. Age: Early Jurassic, 175 to 202 million years old. About 3 mi of the line.
Basalt. Age: Early Jurassic, 175 to 202 million years old. About 2 mi of the line.
Siltstone, shale. Age: Jurassic, 145 to 202 million years old. About 1 mi of the line.
Siltstone, sandstone. Age: Early Jurassic, 175 to 202 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. 2 smaller units along the line are not listed.
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.
A raindrop that lands in Opal reaches Chesapeake Bay and the Atlantic Ocean by way of Tinpot Run and the Rappahannock: about 150 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Opal; river miles along the main stem, rounded.
