The Tri-City 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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76° on Nov. 13, 1995, the hottest reading for this week of the year since 1899. Next is 74° in 1999.
Tri-City’s center stands about 890 ft above sea level. Within three miles the land runs from 610 ft to 2,340 ft, a difference of 1,730 ft: steep hill country. The highest named summit within 15 miles is Silver Butte, about 3,960 ft, 9 miles south-southwest.
Under the town center the state geologic map shows Myrtle Group (siltstone, sandstone), from the Late Jurassic to Early Cretaceous, 125 to 153 million years old.
The section below crosses 7 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.
Siltstone, sandstone. Age: Late Jurassic to Early Cretaceous, 125 to 153 million years old. About 11 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Graywacke, mudstone. Age: Late Jurassic to Early Cretaceous, 129 to 153 million years old. About 3 mi of the line.
Andesite. Age: Late Jurassic, 145 to 164 million years old. About 3 mi of the line.
Basalt. Age: Late Jurassic to Early Cretaceous, 100 to 164 million years old. About 2 mi of the line.
Peridotite, serpentinite. Age: Paleozoic to Jurassic, 145 to 542 million 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. 1 smaller unit along the line are not listed.
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 Tri-City reaches the Pacific Ocean by way of the South Umpqua and the Umpqua: about 150 river miles.
110 miles of the trip are on the Umpqua.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Tri-City; river miles along the main stem, rounded.
Tri-City has a warm-summer Mediterranean climate. Summer afternoons average 89° in August; winter nights fall to about 37° in January. About 31 inches of rain fall in a normal year, with about 2 inches of snow.
On November 14 Tri-City normally reaches 58° and falls to 41°. The record high is 70°, in 1999; the record low 13°, in 1978. The most rain on this date, 1.99 in, fell in 1958.
Normals 1991–2020 and records since 1899 at Riddle, 3 miles southwest, 210 ft lower. NOAA, through RCC-ACIS.
