The San Ysidro 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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74° on Nov. 16, 2025, the hottest reading for this week of the year since 1953. Next is 73° in 2005.
San Ysidro’s center stands about 5,470 ft above sea level. Within three miles the land runs from 5,420 ft to 6,320 ft, a difference of 900 ft: hilly country. The highest named summit within 15 miles is Pajarito Peak, about 9,020 ft, 10 miles north-northwest.
Under the town center the state geologic map shows Alluvium (unconsolidated), from the Pleistocene to Holocene, less than 0.1 million years old.
The section below crosses 7 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 6×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Granitic, gneiss. Age: Paleoproterozoic, 1.6 to 1.7 billion years old. About 6 mi of the line.
Unconsolidated. Age: Pleistocene to Holocene, less than 0.1 million years old. About 5 mi of the line.
Conglomerate-sandstone, coarse-detrital, fine-detrital. Age: Late Oligocene to Late Miocene, 5.3 to 28 million years old. About 4 mi of the line.
Sedimentary. Age: Permian, 252 to 299 million years old. About 4 mi of the line.
Mixed-clastic, fine-detrital, coarse-detrital. Age: Late Oligocene to Pleistocene, 0.1 to 28 million years old. About 3 mi of the line.
Sandstone, mudstone, conglomerate. Age: Middle Triassic to Late Triassic, 202 to 247 million years old. About 2 mi of the line.
From the USGS State Geologic Map Compilation (Horton and others, 2017), the states’ geologic maps joined at a common scale. 1 smaller unit 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 San Ysidro reaches the Gulf of America by way of the Jemez and the Rio Grande: about 1,600 river miles.
Lakes on the way: Paz Ramirez Lake, Amistad Reservoir, Elephant Butte Reservoir and Caballo Reservoir.
760 miles of the trip are on the Rio Grande.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of San Ysidro; river miles along the main stem, rounded.
San Ysidro has a cold semi-arid climate. Summer afternoons average 93° in July; winter nights fall to about 22° in January. A normal year brings about 6 inches of snow; with the rain, that comes to about 9 inches of water.
On November 14 San Ysidro normally reaches 58° and falls to 29°. The record high is 73°, in 2005; the record low 16°, in 2018. The most rain on this date, 0.12 in, fell in 1961.
Normals 1991–2020 and records since 1953 at Jemez Dam, 18 miles southeast. NOAA, through RCC-ACIS.
