The Mercer Island 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.
Mercer Island’s center stands about 350 ft above sea level. Within three miles the land runs from 10 ft to 430 ft, a difference of 420 ft: hilly country. The highest named summit within 15 miles is Tiger Mountain, about 3,000 ft, 14 miles east-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 8×. 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 8 mi of the line.
Fine-detrital, coarse-detrital. Age: Late Pliocene to Pleistocene, less than 3.6 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, basaltic-andesite. Age: Late Eocene, 34 to 38 million years old. About 1 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 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 Mercer Island reaches Puget Sound and the Pacific Ocean by way of Lake Washington: about 17 river miles.
Lake on the way: Lake Washington.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Mercer Island; river miles along the main stem, rounded.
Mercer Island 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 Mercer Island 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, 8 miles north, 290 ft lower). NOAA, through RCC-ACIS.
