The Pomeroy 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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Pomeroy’s center stands about 1,870 ft above sea level. Within three miles the land runs from 1,760 ft to 2,780 ft, a difference of 1,020 ft: steep hill country. The highest named summit within 15 miles is Calloway Hill, about 3,720 ft, 7 miles south.
Under the town center the state geologic map shows Miocene volcanic rocks (basalt), from the Late Oligocene to Early Pliocene, 3.6 to 28 million years old.
The section below crosses 2 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.
Basalt. Age: Late Oligocene to Early Pliocene, 3.6 to 28 million years old. About 12 mi of the line.
Silt. Age: Pleistocene, less than 2.6 million years old. About 12 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale.
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 Pomeroy reaches the Pacific Ocean by way of Pataha Creek, the Tucannon, the Snake and the Columbia: about 420 river miles.
Lake on the way: Lake Umatilla.
210 miles of the trip are on the Columbia.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Pomeroy; river miles along the main stem, rounded.
