The Alpine 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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91° on Nov. 12, 1974, the hottest reading for this week of the year since 1951. Next is 91° in 2008.
Alpine’s center stands about 1,860 ft above sea level. Within three miles the land runs from 900 ft to 3,710 ft, a difference of 2,810 ft: mountain country. The highest named summit within 15 miles is Cuyamaca Peak, about 6,480 ft, 12 miles northeast.
Under the town center the state geologic map shows Mesozoic granitic rocks, unit 2 (Peninsular Ranges) (tonalite), from the Middle Jurassic to Late Cretaceous, 66 to 175 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 5×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Tonalite. Age: Middle Jurassic to Late Cretaceous, 66 to 175 million years old. About 17 mi of the line.
Schist, gneiss. Age: Paleoproterozoic to Cretaceous, 66 to 2,500 million years old. About 3 mi of the line.
Diorite, gabbro. Age: Triassic to Cretaceous, 66 to 252 million years old. About 2 mi of the line.
Plutonic, gneiss. Age: Paleoproterozoic to Late Cretaceous, 66 to 2,500 million years old. About 1 mi of the line.
Pelitic-schist. Age: Triassic, 202 to 252 million years old. About 0.7 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 0.2 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 Alpine reaches the Pacific Ocean by way of Alpine Creek and the San Diego: about 35 river miles.
Often dry. About 80% of the way is mapped as streams that run only after rain or snowmelt; the water makes the whole trip in floods.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Alpine; river miles along the main stem, rounded.
Alpine has a hot-summer Mediterranean climate. Summer afternoons average 89° in August; winter nights fall to about 42° in February. About 16 inches of rain fall in a normal year.
On November 14 Alpine normally reaches 71° and falls to 48°. The record high is 91°, in 2008; the record low 32°, in 1964. The most rain on this date, 1.03 in, fell in 1993.
Normals 1991–2020 and records since 1951 at Alpine, here, 160 ft lower. NOAA, through RCC-ACIS.
