The Lake Forest 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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26° on Nov. 12, 1938, the coldest reading for this week of the year since 1906. Next is 30° in 1919.
Lake Forest’s center stands about 470 ft above sea level. Within three miles the land runs from 250 ft to 890 ft, a difference of 640 ft: hilly country. The highest named summit within 15 miles is Santiago Peak, about 5,660 ft, 10 miles east-northeast.
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 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.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 10 mi of the line.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 4 mi of the line.
Felsic-volcanic, mafic-volcanic. Age: Late Jurassic to Early Cretaceous, 100 to 164 million years old. About 4 mi of the line.
Sandstone, siltstone-mudstone. Age: Late Cretaceous, 66 to 100 million years old. About 2 mi of the line.
Argillite. Age: Paleozoic to Late Jurassic, 145 to 542 million years old. About 1 mi of the line.
Sandstone, mudstone. Age: Miocene to Pleistocene, less than 23 million years old. About 1 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 Lake Forest reaches the Pacific Ocean by way of Serrano Creek and San Diego Creek: about 15 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 Lake Forest; river miles along the main stem, rounded.
Lake Forest has a hot semi-arid climate. Summer afternoons average 85° in August; winter nights fall to about 48° in December. About 12 inches of rain fall in a normal year.
On November 14 Lake Forest normally reaches 75° and falls to 53°. The record high is 100°, in 1933; the record low 30°, in 1938. The most rain on this date, 1.83 in, fell in 1946.
Normals 1991–2020 and records since 1906 at Santa Ana Fire Station, 12 miles west-northwest, 340 ft lower. NOAA, through RCC-ACIS.
