The Black Diamond 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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3.80 inches of rain fell in two days, the most for this week of the year since records began in 1945. The next wettest, 3.18 inches, fell in 2015.
Black Diamond’s center stands about 670 ft above sea level. Within three miles the land runs from 200 ft to 1,200 ft, a difference of 1,000 ft: steep hill country. The highest named summit within 15 miles is Rattlesnake Mountain, about 3,500 ft, 14 miles northeast.
Under the town center the state geologic map shows Younger glacial drift (fine-detrital, coarse-detrital), from the Pleistocene, less than 2.6 million 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 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.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 9 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 6 mi of the line.
Andesite. Age: Oligocene to Middle Miocene, 12 to 34 million years old. About 6 mi of the line.
Sandstone. Age: Early Eocene to Middle Eocene, 38 to 56 million years old. About 3 mi of the line.
Silt, sand. Age: Holocene, less than 12,000 years old. About 0.9 mi of the line.
Fine-detrital, coarse-detrital. Age: Late Pliocene to Pleistocene, less than 3.6 million years old. About 0.5 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 Black Diamond reaches Puget Sound and the Pacific Ocean by way of Covington Creek, Big Soos Creek, the Green River, the Duwamish and the Duwamish Waterway: about 45 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Black Diamond; river miles along the main stem, rounded.
Black Diamond has a warm-summer Mediterranean climate. Summer afternoons average 78° in August; winter nights fall to about 37° in December. A normal year brings about 6 inches of snow; with the rain, that comes to about 39 inches of water.
On November 14 Black Diamond normally reaches 52° and falls to 41°. The record high is 65°, in 1995; the record low 9°, in 1955. The most rain on this date, 2.61 in, fell in 2001.
Normals 1991–2020 and records since 1945 from the Seattle Tacoma Area threaded record (Seattle Tacoma Airport, 17 miles west-northwest, 300 ft lower). NOAA, through RCC-ACIS.
