The Ketchum 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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68° on Nov. 15, 1999, the hottest reading for this week of the year since 1937. Next is 66° in 2016.
Ketchum’s center stands about 5,850 ft above sea level. Within three miles the land runs from 5,690 ft to 8,710 ft, a difference of 3,020 ft: mountain country. The highest named summit within 15 miles is Hyndman Peak, about 11,890 ft, 13 miles east-northeast.
Under the town center the state geologic map shows Alluvial deposits (gravel, sand, silt), from the Quaternary, less than 2.6 million years old.
The section below crosses 6 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.
Age: Carboniferous to Permian, 252 to 324 million years old. About 10 mi of the line.
Dacite, andesite, rhyolite. Age: Eocene, 34 to 56 million years old. About 5 mi of the line.
Dolostone, limestone, sandstone. Age: Ordovician to Devonian, 359 to 487 million years old. About 5 mi of the line.
Limestone, dolostone. Age: Cambrian to Ordovician, 445 to 542 million years old. About 2 mi of the line.
Gravel, sand, silt. Age: Quaternary, less than 2.6 million years old. About 2 mi of the line.
Granodiorite, granite. Age: Early Cretaceous to Late Cretaceous, 67 to 107 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.
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 Ketchum reaches the Pacific Ocean by way of the Big Wood, the Malad, the Snake and the Columbia: about 1,000 river miles.
Lakes on the way: Lake Umatilla, Brownlee Reservoir, Cove Arm Lake and Magic Reservoir.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Ketchum; river miles along the main stem, rounded.
Ketchum has a dry-summer warm-summer continental climate. Summer afternoons average 80° in July; winter nights fall to about 8° in January. A normal year brings about 102 inches of snow; with the rain, that comes to about 17 inches of water.
On November 14 Ketchum normally reaches 42° and falls to 18°. The record high is 65°, in 1999; the record low −6°, in 1964. The most rain on this date, 0.82 in, fell in 1988.
Normals 1991–2020 and records since 1937 at Ketchum Ranger Station, here. NOAA, through RCC-ACIS.
