The Bonsall 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.
Bonsall’s center stands about 180 ft above sea level. Within three miles the land runs from 130 ft to 750 ft, a difference of 620 ft: hilly country. The highest named summit within 15 miles is Margarita Peak, about 3,160 ft, 14 miles northwest.
Under the town center the state geologic map shows Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene to Holocene, less than 2.6 million years old.
The section below crosses 5 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 9×. 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 12 mi of the line.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 million years old. About 6 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 3 mi of the line.
Argillite. Age: Paleozoic to Late Jurassic, 145 to 542 million years old. About 2 mi of the line.
Siltstone-mudstone. Age: Early Cretaceous to Late Cretaceous, 66 to 145 million years old. About 0.8 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 Bonsall reaches the Pacific Ocean by way of the San Luis Rey: about 16 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 Bonsall; river miles along the main stem, rounded.
Bonsall 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 Bonsall 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, 4 miles south, 250 ft higher. NOAA, through RCC-ACIS.
