The Riverside 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 1895. Next is 69° in 1954.
Riverside’s center stands about 4,460 ft above sea level. Within three miles the land runs from 4,430 ft to 4,480 ft, a difference of 50 ft: nearly flat ground. The highest named summit within 15 miles is Stevens Peak, about 5,310 ft, 8 miles east-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 29×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Basalt. Age: Late Pliocene to Pleistocene, less than 3 million years old. About 15 mi of the line.
Gravel, sand, silt. Age: Quaternary, less than 2.6 million years old. About 8 mi of the line.
Silt. Age: Pleistocene, less than 2.6 million years old. About 1 mi of the line.
Fine-detrital. Age: Quaternary, less than 2.6 million years old. About 0.4 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 Riverside reaches the Pacific Ocean by way of Watson Slough, the Snake and the Columbia: about 1,080 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 Riverside; river miles along the main stem, rounded.
Riverside has a cold semi-arid climate. Summer afternoons average 87° in July; winter nights fall to about 17° in January. A normal year brings about 15 inches of snow; with the rain, that comes to about 12 inches of water.
On November 14 Riverside normally reaches 46° and falls to 26°. The record high is 67°, in 2025; the record low 3°, in 1916. The most rain on this date, 0.41 in, fell in 2014.
Normals 1991–2020 and records since 1895 at Blackfoot Fire Department, 5 miles east. NOAA, through RCC-ACIS.
