The Index 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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72° on Nov. 11, 2016, the hottest reading for this week of the year since 1924. Next is 69° in 1990.
Index’s center stands about 560 ft above sea level. Within three miles the land runs from 420 ft to 4,740 ft, a difference of 4,320 ft: mountain country. The highest named summit within 15 miles is Kyes Peak, about 7,110 ft, 14 miles northeast.
The section below crosses 11 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 4×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granodiorite, granite. Age: Early Paleocene to Middle Miocene, 12 to 66 million years old. About 10 mi of the line.
Argillite, graywacke. Age: Late Jurassic to Early Cretaceous, 100 to 164 million years old. About 6 mi of the line.
Silt, sand. Age: Holocene, less than 12,000 years old. About 2 mi of the line.
Fine-detrital, coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Chert, metavolcanic. Age: Paleozoic to Paleocene, 56 to 542 million years old. About 0.9 mi of the line.
Phyllite. Age: Jurassic to Early Cretaceous, 100 to 202 million years old. About 0.9 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 5 smaller units 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 Index reaches Puget Sound and the Pacific Ocean by way of the North Fork Skykomish, the Skykomish and the Snohomish: about 50 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Index; river miles along the main stem, rounded.
Index has a warm-summer Mediterranean climate. Summer afternoons average 78° in July; winter nights fall to about 34° in January. About 68 inches of rain fall in a normal year.
On November 14 Index normally reaches 52° and falls to 37°. The record high is 65°, in 1967; the record low 6°, in 1955. The most rain on this date, 2.30 in, fell in 1948.
Normals 1991–2020 and records since 1924 at Startup 1 E, 8 miles west-northwest, 390 ft lower. NOAA, through RCC-ACIS.
