The Fallbrook 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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96° on Nov. 12, 2021, the hottest reading for this week of the year since 1957. Next is 92° in 2008.
Fallbrook’s center stands about 680 ft above sea level. Within three miles the land runs from 260 ft to 1,080 ft, a difference of 820 ft: hilly country. The highest named summit within 15 miles is Margarita Peak, about 3,160 ft, 9 miles west-northwest.
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 3 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.
Tonalite. Age: Middle Jurassic to Late Cretaceous, 66 to 175 million years old. About 20 mi of the line.
Diorite, gabbro. Age: Triassic to Cretaceous, 66 to 252 million years old. About 3 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 0.4 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 Fallbrook reaches the Pacific Ocean by way of the San Luis Rey: about 20 river miles.
Often dry. About 100% 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 Fallbrook; river miles along the main stem, rounded.
Fallbrook has a cold semi-arid climate. Summer afternoons average 81° in August; winter nights fall to about 45° in December. About 13 inches of rain fall in a normal year.
On November 14 Fallbrook normally reaches 72° and falls to 50°. The record high is 90°, in 2008; the record low 34°, in 1964. The most rain on this date, 0.49 in, fell in 1988.
Normals 1991–2020 and records since 1957 at Vista, 10 miles south, 250 ft lower. NOAA, through RCC-ACIS.
