The Lewiston 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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78° on Nov. 11, 2019, the hottest reading for this week of the year since 1974. Next is 72° in 1995.
Lewiston’s center stands about 1,830 ft above sea level. Within three miles the land runs from 1,760 ft to 3,750 ft, a difference of 1,990 ft: steep hill country. The highest named summit within 15 miles is Granite Peak, about 8,010 ft, 14 miles north-northwest.
Under the town center the state geologic map shows Paleozoic metavolcanic rocks, unit 1 (Eastern Klamath Mountains) (mafic-volcanic), from the Permian, 252 to 299 million years old.
The section below crosses 5 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.
Diorite. Age: Jurassic to Early Cretaceous, 100 to 202 million years old. About 14 mi of the line.
Sandstone. Age: Oligocene to Miocene, 5.3 to 34 million years old. About 5 mi of the line.
Mafic-volcanic. Age: Permian, 252 to 299 million years old. About 3 mi of the line.
Amphibolite, schist. Age: Devonian, 359 to 422 million years old. About 2 mi of the line.
Mudstone, volcanic. Age: Carboniferous to Permian, 273 to 359 million years old. About 0.4 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 Lewiston reaches the Pacific Ocean by way of the Trinity and the Klamath: about 150 river miles.
110 miles of the trip are on the Trinity.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Lewiston; river miles along the main stem, rounded.
Lewiston has a hot-summer Mediterranean climate. Summer afternoons average 96° in July; winter nights fall to about 32° in December. A normal year brings about 6 inches of snow; with the rain, that comes to about 32 inches of water.
On November 14 Lewiston normally reaches 59° and falls to 36°. The record high is 72°, in 2013; the record low 21°, in 1985. The most rain on this date, 1.04 in, fell in 1981.
Normals 1991–2020 and records since 1974 at Trinity River Hatchery, here. NOAA, through RCC-ACIS.
