The Half Moon Bay 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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82° on Nov. 16, 2008, the hottest reading for this week of the year since 1939. Next is 80° in 2005.
Half Moon Bay’s center stands about 70 ft above sea level. Within three miles the land runs from 10 ft to 1,030 ft, a difference of 1,020 ft: steep hill country. Open water lies within three miles. The highest named summit within 15 miles is Morena Sierra, about 2,450 ft, 8 miles east-southeast.
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 6 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.
Mudstone, sandstone. Age: Paleocene to Oligocene, 23 to 66 million years old. About 4 mi of the line.
Sandstone, mudstone. Age: Oligocene to Pliocene, 2.6 to 34 million years old. About 3 mi of the line.
Sandstone, mudstone. Age: Miocene to Pleistocene, less than 23 million years old. About 3 mi of the line.
Coarse-detrital. Age: Pleistocene, less than 2.6 million years old. About 2 mi of the line.
Sandstone, conglomerate. Age: Miocene to Pleistocene, less than 23 million years old. About 1 mi of the line.
Sandstone, mudstone. Age: Jurassic to Cretaceous, 66 to 202 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.
Rain that falls on Half Moon Bay runs straight into the Pacific Ocean.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of Half Moon Bay; river miles along the main stem, rounded.
Half Moon Bay has a warm-summer Mediterranean climate. Summer afternoons average 66° in August; winter nights fall to about 43° in January. About 26 inches of rain fall in a normal year.
On November 14 Half Moon Bay normally reaches 63° and falls to 45°. The record high is 76°, in 2021; the record low 34°, in 2022. The most rain on this date, 1.80 in, fell in 1953.
Normals 1991–2020 and records since 1939 at Half Moon Bay, here. NOAA, through RCC-ACIS.
