The American Falls 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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74° on Nov. 13, 1999, the hottest reading for this week of the year since 1973. Next is 72° in 1989.
American Falls’s center stands about 4,410 ft above sea level. Within three miles the land runs from 4,250 ft to 4,880 ft, a difference of 630 ft: hilly country. The highest named summit within 15 miles is Bannock Peak, about 8,220 ft, 14 miles south-southeast.
Under the town center the state geologic map shows Fluvial and lake sediment (fine-detrital), from the Quaternary, less than 2.6 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 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.
Fine-detrital. Age: Quaternary, less than 2.6 million years old. About 7 mi of the line.
Basalt. Age: Late Pliocene to Pleistocene, less than 3 million years old. About 6 mi of the line.
Age: Carboniferous to Permian, 252 to 324 million years old. About 5 mi of the line.
Silt. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Basalt. Age: Middle Miocene to Late Pliocene, 3 to 15 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.
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 American Falls reaches the Pacific Ocean by way of American Falls Reservoir, the Snake and the Columbia: about 1,030 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 American Falls; river miles along the main stem, rounded.
American Falls has a dry-summer warm-summer continental climate. Summer afternoons average 89° in July; winter nights fall to about 17° in January. About 14 inches of rain fall in a normal year.
On November 14 American Falls normally reaches 47° and falls to 24°. The record high is 71°, in 1999; the record low 2°, in 1978. The most rain on this date, 0.79 in, fell in 2006.
Normals 1991–2020 and records since 1973 at Massacre Rocks State Park, 11 miles southwest, 220 ft lower. NOAA, through RCC-ACIS.
