The Monmouth 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. 13, 1999, the hottest reading for this week of the year since 1892. Next is 68° in 1930.
Monmouth’s center stands about 200 ft above sea level. Within three miles the land runs from 140 ft to 520 ft, a difference of 380 ft: rolling country. The highest named summit within 15 miles is Mount Sykes, about 2,090 ft, 13 miles west.
Under the town center the state geologic map shows Lacustrine and fluvial sedimentary rocks (clay, silt, sand), from the Pleistocene, less than 2.6 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 10×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Clay, silt, sand. Age: Pleistocene, less than 2.6 million years old. About 6 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 4 mi of the line.
Basalt. Age: Paleocene to Middle Eocene, 38 to 66 million years old. About 4 mi of the line.
Siltstone. Age: Middle Eocene to Late Eocene, 34 to 48 million years old. About 3 mi of the line.
Sandstone. Age: Oligocene to Early Miocene, 16 to 34 million years old. About 3 mi of the line.
Mudstone. Age: Middle Eocene to Late Eocene, 34 to 48 million years old. About 3 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 Monmouth reaches the Pacific Ocean by way of Middle Fork Ash Creek, Ash Creek, the Willamette and the Columbia: about 200 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 Monmouth; river miles along the main stem, rounded.
Monmouth has a warm-summer Mediterranean climate. Summer afternoons average 84° in July; winter nights fall to about 35° in December. About 40 inches of rain fall in a normal year.
On November 14 Monmouth normally reaches 54° and falls to 39°. The record high is 68°, in 2001; the record low 12°, in 1955. The most rain on this date, 3.00 in, fell in 1896.
Normals 1991–2020 and records since 1892 from the Salem Area threaded record (Salem Airport (Mcnary Field), 12 miles east-northeast). NOAA, through RCC-ACIS.
