The Lucas Valley-Marinwood 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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82° on Nov. 14, 2008, the hottest reading for this week of the year since 1894. Next is 82° in 2010.
Lucas Valley-Marinwood’s center stands about 740 ft above sea level. Within three miles the land runs from 10 ft to 1,660 ft, a difference of 1,650 ft: steep hill country. The highest named summit within 15 miles is Mount Tamalpais, about 2,570 ft, 8 miles south.
Under the town center the state geologic map shows Franciscan Complex, unit 1 (Coast Ranges) (sandstone, mudstone), from the Jurassic to Cretaceous, 66 to 202 million years old.
The section below crosses 9 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 11×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Melange. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 6 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 5 mi of the line.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 5 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 2 mi of the line.
Greenstone. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 1 mi of the line.
Siltstone-mudstone. Age: Early Cretaceous, 113 to 145 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. 3 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 Lucas Valley-Marinwood reaches San Francisco Bay and the Pacific Ocean by way of Miller Creek: about 6 river miles.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Lucas Valley-Marinwood; river miles along the main stem, rounded.
Lucas Valley-Marinwood has a warm-summer Mediterranean climate. Summer afternoons average 81° in July; winter nights fall to about 42° in December. About 34 inches of rain fall in a normal year.
On November 14 Lucas Valley-Marinwood normally reaches 65° and falls to 46°. The record high is 82°, in 2008; the record low 30°, in 1894. The most rain on this date, 2.10 in, fell in 1953.
Normals 1991–2020 and records since 1894 at San Rafael-Civic Center, 4 miles southeast, 620 ft lower. NOAA, through RCC-ACIS.
