The Greenhorn 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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Greenhorn’s center stands about 6,300 ft above sea level. Within three miles the land runs from 5,000 ft to 7,580 ft, a difference of 2,580 ft: mountain country. The highest named summit within 15 miles is Mount Ireland, about 8,250 ft, 12 miles northeast.
Under the town center the state geologic map shows Sedimentary rocks, partly metamorphosed (limestone, arenite, argillite), from the Devonian to Carboniferous, 299 to 422 million years old.
The section below crosses 10 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 5×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Quartz-diorite, granitic, granodiorite. Age: Late Triassic to Late Cretaceous, 66 to 208 million years old. About 5 mi of the line.
Andesite. Age: Paleocene to Early Oligocene, 28 to 66 million years old. About 5 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 3 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 3 mi of the line.
Argillite, chert, phyllite. Age: Permian to Triassic, 202 to 299 million years old. About 3 mi of the line.
Limestone, arenite, argillite. Age: Devonian to Carboniferous, 299 to 422 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 4 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 Greenhorn reaches the Pacific Ocean by way of Greenhorn Creek, the North Fork Burnt, the Burnt, the Snake and the Columbia: about 750 river miles.
Lakes on the way: Lake Umatilla, Brownlee Reservoir and Hells Canyon Reservoir.
240 miles of the trip are on the Snake.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Greenhorn; river miles along the main stem, rounded.
