The Afton 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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Afton’s center stands about 6,250 ft above sea level. Within three miles the land runs from 6,060 ft to 8,650 ft, a difference of 2,590 ft: mountain country. The highest named summit within 15 miles is Mount Fitzpatrick, about 10,840 ft, 8 miles east.
Under the town center the state geologic map shows Alluvium and Colluvium (clay, silt, sand), from the Pleistocene to Holocene, less than 2.6 million years old.
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 4×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Clay, silt, sand. Age: Pleistocene to Holocene, less than 2.6 million years old. About 9 mi of the line.
Shale, limestone, siltstone. Age: Early Triassic to Late Triassic, 202 to 252 million years old. About 6 mi of the line.
Sandstone, shale. Age: Cretaceous, 66 to 145 million years old. About 4 mi of the line.
Sandstone. Age: Triassic to Jurassic, 145 to 252 million years old. About 2 mi of the line.
Siltstone, sandstone, limestone. Age: Middle Jurassic to Late Jurassic, 145 to 175 million years old. About 2 mi of the line.
Black-shale, sandstone, siltstone. Age: Early Cretaceous, 100 to 145 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 Afton reaches the Pacific Ocean by way of Swift Creek, the Salt River, the Snake and the Columbia: about 1,280 river miles.
Lakes on the way: American Falls Reservoir, Palisades Reservoir, Lake Umatilla and Brownlee Reservoir.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Afton; river miles along the main stem, rounded.
