The Grand Coulee 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, 2021, the hottest reading for this week of the year since 1934. Next is 62° in 1953.
Grand Coulee’s center stands about 1,530 ft above sea level. Within three miles the land runs from 980 ft to 2,420 ft, a difference of 1,440 ft: steep hill country. The highest named summit within 15 miles is Keller Butte, about 4,790 ft, 13 miles northeast.
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 9×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granite. Age: Precambrian to Eocene. About 10 mi of the line.
Silt. Age: Pleistocene, less than 2.6 million years old. About 3 mi of the line.
Basalt. Age: Late Oligocene to Early Pliocene, 3.6 to 28 million years old. About 3 mi of the line.
Andesite, dacite. Age: Eocene to Oligocene, 23 to 56 million years old. About 2 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 0.9 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 Grand Coulee reaches the Pacific Ocean by way of the Columbia: about 590 river miles.
Lake on the way: Lake Umatilla.
320 miles of the trip are on the Columbia.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grand Coulee; river miles along the main stem, rounded.
Grand Coulee has a cold semi-arid climate. Summer afternoons average 88° in July; winter nights fall to about 23° in January. About 11 inches of rain fall in a normal year.
On November 14 Grand Coulee normally reaches 43° and falls to 31°. The record high is 63°, in 2021; the record low 1°, in 1955. The most rain on this date, 0.55 in, fell in 1963.
Normals 1991–2020 and records since 1934 at Coulee Dam 1 SW, here, 190 ft higher. NOAA, through RCC-ACIS.
