The Sammamish 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. 14, 1995, the hottest reading for this week of the year since 1894. Next is 66° in 1905.
Sammamish’s center stands about 520 ft above sea level. Within three miles the land runs from 20 ft to 590 ft, a difference of 570 ft: hilly country. The highest named summit within 15 miles is Rattlesnake Mountain, about 3,500 ft, 15 miles southeast.
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 5 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.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 14 mi of the line.
Andesite, basaltic-andesite. Age: Late Eocene, 34 to 38 million years old. About 4 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 3 mi of the line.
Silt, sand. Age: Holocene, less than 12,000 years old. About 2 mi of the line.
Andesite, basalt. Age: Eocene to Oligocene, 23 to 56 million years old. About 0.7 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 Sammamish reaches Puget Sound and the Pacific Ocean by way of Pine Lake Creek and the Sammamish: about 40 river miles.
Lakes on the way: Lake Washington and Lake Sammamish.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Sammamish; river miles along the main stem, rounded.
Sammamish has a warm-summer Mediterranean climate. Summer afternoons average 77° in August; winter nights fall to about 37° in January. About 38 inches of rain fall in a normal year, with about 4 inches of snow.
On November 14 Sammamish normally reaches 52° and falls to 41°. The record high is 70°, in 1995; the record low 15°, in 1955. The most rain on this date, 2.27 in, fell in 1906.
Normals 1991–2020 and records since 1894 from the Seattle City Area threaded record (Seattle Sand Point Wfo, 12 miles west-northwest, 460 ft lower). NOAA, through RCC-ACIS.
