The Johannesburg 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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Johannesburg’s center stands about 3,590 ft above sea level. Within three miles the land runs from 2,860 ft to 4,500 ft, a difference of 1,640 ft: steep hill country. The highest named summit within 15 miles is Red Mountain, about 5,220 ft, 4 miles east-southeast.
Under the town center the state geologic map shows Schist of various types and ages, unit 2 (Southern and West-central California) (mica-schist), from the Late Cretaceous to Eocene, 34 to 100 million years old.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 13 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 4 mi of the line.
Argillite, chert, phyllite. Age: Cambrian to Jurassic, 145 to 542 million years old. About 2 mi of the line.
Mica-schist. Age: Late Cretaceous to Eocene, 34 to 100 million years old. About 2 mi of the line.
Rhyolite, basalt. Age: Early Miocene to Early Pliocene, 4 to 22 million years old. About 1 mi of the line.
Greenstone, andesite. Age: Devonian to Permian, 252 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. 1 smaller unit 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.
