The Post Mountain 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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Post Mountain’s center stands about 3,320 ft above sea level. Within three miles the land runs from 2,960 ft to 4,330 ft, a difference of 1,370 ft: steep hill country. The highest named summit within 15 miles is Chanchelulla Peak, about 6,350 ft, 13 miles east-northeast.
Under the town center the state geologic map shows Paleozoic marine rocks, undivided, unit 9 (Western Klamath Mountains) (melange), from the Devonian to Jurassic, 145 to 422 million years old.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 6×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Melange. Age: Devonian to Jurassic, 145 to 422 million years old. About 10 mi of the line.
Mica-schist. Age: Early Cretaceous, 110 to 143 million years old. About 4 mi of the line.
Slate, graywacke. Age: Triassic to Late Jurassic, 145 to 252 million years old. About 3 mi of the line.
Sandstone. Age: Oligocene to Miocene, 5.3 to 34 million years old. About 2 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 2 mi of the line.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 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. 3 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 Post Mountain reaches the Pacific Ocean by way of Post Creek, Rattlesnake Creek, the South Fork Trinity, the Trinity and the Klamath: about 140 river miles.
55 miles of the trip are on the South Fork Trinity.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Post Mountain; river miles along the main stem, rounded.
