The Placentia 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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95° on Nov. 13, 2007, the hottest reading for this week of the year since 1989. Next is 95° in 2016.
Placentia’s center stands about 260 ft above sea level. Within three miles the land runs from 160 ft to 430 ft, a difference of 270 ft: rolling country. The highest named summit within 15 miles is Sierra Peak, about 3,030 ft, 13 miles east.
Under the town center the state geologic map shows Older Quaternary alluvium and marine deposits (coarse-detrital), from the Pleistocene, less than 2.6 million years old.
The section below crosses 4 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 12 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 6 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 4 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.
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 Placentia reaches the Pacific Ocean by way of Carbon Creek, Coyote Creek and the San Gabriel: about 17 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 Placentia; river miles along the main stem, rounded.
Placentia has a hot semi-arid climate. Summer afternoons average 89° in August; winter nights fall to about 48° in December. About 14 inches of rain fall in a normal year.
On November 14 Placentia normally reaches 77° and falls to 53°. The record high is 94°, in 2007; the record low 39°, in 2000. The most rain on this date, 0.86 in, fell in 2025.
Normals 1991–2020 and records since 1989 at Anaheim, here. NOAA, through RCC-ACIS.
