The Ammon 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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70° on Nov. 15, 1999, the hottest reading for this week of the year since 1952. Next is 66° in 1953.
Ammon’s center stands about 4,720 ft above sea level. Within three miles the land runs from 4,690 ft to 5,050 ft, a difference of 360 ft: rolling country. The highest named summit within 15 miles is Birch Creek Mountain, about 7,470 ft, 13 miles south-southeast.
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 4 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 8×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Gravel, sand, silt. Age: Quaternary, less than 2.6 million years old. About 13 mi of the line.
Rhyolite. Age: Late Miocene to Late Pliocene, 3 to 6.6 million years old. About 8 mi of the line.
Sandstone, shale. Age: Cretaceous, 66 to 145 million years old. About 2 mi of the line.
Sandstone, limestone. Age: Jurassic, 145 to 202 million years old. About 0.7 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 Ammon reaches the Pacific Ocean by way of Sand Creek, the Reservation Canal, the Blackfoot, the Snake and the Columbia: about 1,120 river miles.
Lakes on the way: American Falls Reservoir, Lake Umatilla, Brownlee Reservoir and Cove Arm Lake.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Ammon; river miles along the main stem, rounded.
Ammon has a warm-summer humid continental climate. Summer afternoons average 86° in July; winter nights fall to about 16° in January. About 14 inches of rain fall in a normal year.
On November 14 Ammon normally reaches 44° and falls to 26°. The record high is 64°, in 1999; the record low −4°, in 1978. The most rain on this date, 0.55 in, fell in 1957.
Normals 1991–2020 and records since 1952 at Idaho Falls - Kifi, 4 miles northwest. NOAA, through RCC-ACIS.
