The Walnut Park 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. 13, 1933, the hottest reading for this week of the year since 1877. Next is 94° in 1900.
Walnut Park’s center stands about 150 ft above sea level. Within three miles the land runs from 90 ft to 210 ft, a difference of 120 ft: gently rolling country. The highest named summit within 15 miles is Flint Peak, about 1,840 ft, 14 miles north.
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 13×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Coarse-detrital. Age: Pleistocene to Holocene, less than 2.6 million years old. About 16 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 3 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 3 mi of the line.
Plutonic. Age: Jurassic to Cretaceous, 66 to 202 million years old. About 1 mi of the line.
Sandstone, mudstone. Age: Miocene to Pleistocene, less than 23 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 Walnut Park reaches the Pacific Ocean by way of Compton Creek and the Los Angeles: about 10 river miles.
Often dry. About 80% 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 Walnut Park; river miles along the main stem, rounded.
Walnut Park has a hot semi-arid climate. Summer afternoons average 84° in August; winter nights fall to about 48° in December. About 14 inches of rain fall in a normal year.
On November 14 Walnut Park normally reaches 73° and falls to 54°. The record high is 93°, in 1933; the record low 36°, in 1880. The most rain on this date, 1.33 in, fell in 1928.
Normals 1991–2020 and records since 1877 from the Los Angeles Downtown Area threaded record (Los Angeles Downtown, 7 miles north, 230 ft higher). NOAA, through RCC-ACIS.
