The Idaho City 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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3° on Nov. 15, 2014, the coldest reading for this week of the year since 1973. Next is 12° in 1978.
Idaho City’s center stands about 3,960 ft above sea level. Within three miles the land runs from 3,850 ft to 5,350 ft, a difference of 1,500 ft: steep hill country. The highest named summit within 15 miles is Pilot Peak, about 8,100 ft, 12 miles northeast.
The section below crosses 4 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.
Granodiorite, granite. Age: Early Cretaceous to Late Cretaceous, 67 to 107 million years old. About 20 mi of the line.
Mixed-clastic. Age: Early Miocene to Late Miocene, 8 to 17 million years old. About 2 mi of the line.
Granodiorite, quartz-monzodiorite, granite. Age: Early Eocene to Middle Eocene, 43 to 49 million years old. About 0.8 mi of the line.
Gravel, sand, silt. Age: Quaternary, less than 2.6 million years old. About 0.6 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 Idaho City reaches the Pacific Ocean by way of Elk Creek, Mores Creek, the Boise, the Snake and the Columbia: about 810 river miles.
Lakes on the way: Lake Umatilla, Brownlee Reservoir, Arrowrock 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 Idaho City; river miles along the main stem, rounded.
Idaho City has a dry-summer hot-summer continental climate. Summer afternoons average 88° in July; winter nights fall to about 23° in January. A normal year brings about 57 inches of snow; with the rain, that comes to about 18 inches of water.
On November 14 Idaho City normally reaches 47° and falls to 30°. The record high is 61°, in 2025; the record low 14°, in 1985. The most rain on this date, 0.54 in, fell in 2014.
Normals 1991–2020 and records since 1973 at Boise 7 N, 20 miles west-southwest. NOAA, through RCC-ACIS.
