The Topanga 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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4.43 inches of rain fell in two days, the most for this week of the year since records began in 1949. The next wettest, 3.50 inches, fell in 2025.
Topanga’s center stands about 1,060 ft above sea level. Within three miles the land runs from 610 ft to 2,390 ft, a difference of 1,780 ft: steep hill country. The highest named summit within 15 miles is Castro Peak, about 2,800 ft, 10 miles west.
Under the town center the state geologic map shows Miocene marine rocks (sandstone, mudstone), from the Oligocene to Pliocene, 2.6 to 34 million years old.
The section below crosses 7 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.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 7 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 6 mi of the line.
Sandstone, mudstone. Age: Paleocene, 56 to 66 million years old. About 2 mi of the line.
Sandstone, conglomerate. Age: Middle Eocene to Early Miocene, 16 to 48 million years old. About 2 mi of the line.
Hypabyssal-basalt. Age: Late Oligocene to Late Miocene, 8 to 25 million years old. About 0.7 mi of the line.
Sandstone, siltstone-mudstone. Age: Late Cretaceous, 66 to 100 million years old. About 0.6 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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.
Rain that falls on Topanga runs only a short way, about 4 miles, to the Pacific Ocean.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Topanga; river miles along the main stem, rounded.
Topanga has a hot-summer Mediterranean climate. Summer afternoons average 98° in August; winter nights fall to about 42° in December. About 16 inches of rain fall in a normal year.
On November 14 Topanga normally reaches 77° and falls to 46°. The record high is 96°, in 2021; the record low 25°, in 2000. The most rain on this date, 1.10 in, fell in 1972.
Normals 1991–2020 and records since 1949 at Woodland Hills Pierce College, 6 miles north-northeast, 270 ft lower. NOAA, through RCC-ACIS.
