The Island Park 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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63° on Nov. 14, 1999, the hottest reading for this week of the year since 1937. Next is 61° in 1954.
Island Park’s center stands about 6,430 ft above sea level. Within three miles the land runs from 6,390 ft to 7,200 ft, a difference of 810 ft: hilly country. The highest named summit within 15 miles is Targhee Peak, about 10,220 ft, 13 miles north.
Under the town center the state geologic map shows Alluvial-fan deposits (gravel), from the Quaternary, less than 2.6 million years old.
The section below crosses 9 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.
Rhyolite. Age: Pleistocene, 0.6 to 2 million years old. About 10 mi of the line.
Dacite, andesite, rhyolite. Age: Eocene, 34 to 56 million years old. About 3 mi of the line.
Gravel. Age: Quaternary, less than 2.6 million years old. About 3 mi of the line.
Coarse-detrital, fine-detrital. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Orthogneiss, schist, amphibolite. Age: Neoarchean to Paleoproterozoic, 2.5 to 2.7 billion years old. About 2 mi of the line.
Gravel, sand, silt. Age: Pleistocene to Holocene, less than 1.8 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 3 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 Island Park reaches the Pacific Ocean by way of the Henrys Fork, the Snake and the Columbia: about 1,260 river miles.
Lakes on the way: American Falls Reservoir, Lake Umatilla, Brownlee Reservoir and Bishop Lake.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Island Park; river miles along the main stem, rounded.
Island Park has a dry-summer warm-summer continental climate. Summer afternoons average 77° in July; winter nights fall to about 6° in January. About 29 inches of rain fall in a normal year.
On November 14 Island Park normally reaches 36° and falls to 15°. The record high is 63°, in 1999; the record low −18°, in 1982. The most rain on this date, 0.85 in, fell in 2020.
Normals 1991–2020 and records since 1937 at Island Park, 8 miles south-southwest, 140 ft lower. NOAA, through RCC-ACIS.
