The Yoncalla 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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Partly cloudy
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74° on Nov. 12, 1981, the hottest reading for this week of the year since 1902. Next is 74° in 1999.
Yoncalla’s center stands about 410 ft above sea level. Within three miles the land runs from 330 ft to 1,290 ft, a difference of 960 ft: steep hill country. The highest named summit within 15 miles is Bald Butte, about 3,960 ft, 15 miles east-southeast.
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 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Sandstone. Age: Middle Eocene, 38 to 48 million years old. About 10 mi of the line.
Basalt. Age: Paleocene to Middle Eocene, 38 to 66 million years old. About 6 mi of the line.
Sandstone, siltstone. Age: Late Eocene to Oligocene, 23 to 38 million years old. About 3 mi of the line.
Sandstone. Age: Paleocene to Early Eocene, 48 to 66 million years old. About 3 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 2 mi of the line.
Mudstone. Age: Middle Eocene to Late Eocene, 34 to 48 million years old. About 0.8 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 Yoncalla reaches the Pacific Ocean by way of Yoncalla Creek, Elk Creek and the Umpqua: about 75 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Yoncalla; river miles along the main stem, rounded.
Yoncalla has a warm-summer Mediterranean climate. Summer afternoons average 86° in August; winter nights fall to about 35° in January. About 48 inches of rain fall in a normal year.
On November 14 Yoncalla normally reaches 56° and falls to 39°. The record high is 74°, in 1999; the record low 16°, in 1978. The most rain on this date, 2.35 in, fell in 1941.
Normals 1991–2020 and records since 1902 at Drain, 4 miles north-northwest, 120 ft lower. NOAA, through RCC-ACIS.
