The Hillsboro 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.
Showers likely
Showers likely
Chance of showers
Chance of showers
Chance of showers
Partly cloudy
Partly cloudy
3.65 inches of rain fell in two days, the most for this week of the year since records began in 1929. The next wettest, 3.31 inches, fell in 1973.
Hillsboro’s center stands about 200 ft above sea level. Within three miles the land runs from 130 ft to 210 ft, a difference of 80 ft: gently rolling country. The highest named summit within 15 miles is Bald Mountain, about 1,800 ft, 15 miles north-northwest.
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 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 15×. 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 10 mi of the line.
Basalt. Age: Miocene, 5.3 to 23 million years old. About 5 mi of the line.
Sand, gravel, silt. Age: Holocene, less than 12,000 years old. About 5 mi of the line.
Sandstone-mudstone. Age: Pliocene to Pleistocene, less than 5.3 million years old. About 3 mi of the line.
Sandstone, siltstone. Age: Late Eocene to Early Miocene, 16 to 38 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.
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 Hillsboro reaches the Pacific Ocean by way of Dawson Creek, Rock Creek, the Tualatin, the Willamette and the Columbia: about 170 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 Hillsboro; river miles along the main stem, rounded.
Hillsboro has a warm-summer Mediterranean climate. Summer afternoons average 82° in July; winter nights fall to about 33° in February. About 36 inches of rain fall in a normal year.
On November 14 Hillsboro normally reaches 53° and falls to 37°. The record high is 65°, in 2001; the record low 12°, in 1955. The most rain on this date, 1.35 in, fell in 1948.
Normals 1991–2020 and records since 1929 from the Hillsboro Area threaded record (Portland-Hillsboro Airport, 2 miles northeast). NOAA, through RCC-ACIS.
