The Grand Ronde 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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67° on Nov. 16, 1976, the hottest reading for this week of the year since 1928. Next is 66° in 1939.
Grand Ronde’s center stands about 340 ft above sea level. Within three miles the land runs from 290 ft to 1,310 ft, a difference of 1,020 ft: steep hill country. The highest named summit within 15 miles is Laurel Mountain, about 3,600 ft, 10 miles south.
Under the town center the state geologic map shows Alluvial deposits (sand, gravel, silt), from the Holocene, less than 12,000 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.
Mudstone. Age: Middle Eocene to Late Eocene, 34 to 48 million years old. About 8 mi of the line.
Siltstone. Age: Middle Eocene to Late Eocene, 34 to 48 million years old. About 6 mi of the line.
Gabbro. Age: Oligocene, 23 to 34 million years old. About 5 mi of the line.
Basalt. Age: Paleocene to Middle Eocene, 38 to 66 million years old. About 3 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 1 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 Ronde reaches the Pacific Ocean by way of the South Yamhill, the Yamhill, the Willamette and the Columbia: about 220 river miles.
Lake on the way: Willamette Falls Hydroelectric Power Reservoir.
100 miles of the trip are on the Columbia.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Grand Ronde; river miles along the main stem, rounded.
Grand Ronde has a warm-summer Mediterranean climate. Summer afternoons average 83° in July; winter nights fall to about 35° in January. About 48 inches of rain fall in a normal year.
On November 14 Grand Ronde normally reaches 52° and falls to 39°. The record high is 64°, in 2001; the record low 15°, in 1978. The most rain on this date, 2.00 in, fell in 1941.
Normals 1991–2020 and records since 1928 at Dallas 2 NE, 17 miles east-southeast. NOAA, through RCC-ACIS.
