The La Mesa 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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84° on Nov. 15, 2017, the hottest reading for this week of the year since 1892. Next is 82° in 1899.
La Mesa’s center stands about 3,830 ft above sea level. Within three miles the land runs from 3,820 ft to 4,050 ft, a difference of 230 ft: rolling country. The highest named summit within 15 miles is Bar Mountain, about 6,730 ft, 15 miles north-northeast.
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 6 rock units mapped at the surface.
Heights every 0.1 mile from the Copernicus GLO-90 surface model; vertical exaggeration about 7×. The colored band under the surface is the rock the state geologic map shows at the surface, not a picture of what lies beneath.
Conglomerate-sandstone, coarse-detrital, fine-detrital. Age: Late Miocene to Pleistocene, 0.1 to 7.2 million years old. About 15 mi of the line.
Unconsolidated. Age: Pleistocene to Holocene, less than 0.1 million years old. About 4 mi of the line.
Andesite, basalt. Age: Pleistocene to Holocene, less than 0.8 million years old. About 3 mi of the line.
Unconsolidated. Age: Pleistocene to Holocene, less than 2.6 million years old. About 1 mi of the line.
Felsic-volcanic. Age: Late Eocene to Early Oligocene, 31 to 36 million years old. About 0.9 mi of the line.
Shale, limestone, mixed-clastic. Age: Carboniferous, 299 to 324 million years old. About 0.3 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 La Mesa reaches the Gulf of America by way of the Rio Grande: about 1,280 river miles.
Lakes on the way: Paz Ramirez Lake and Amistad Reservoir.
680 miles of the trip are on the Rio Grande.
Traced down the USGS NHDPlus V2.1 river network from the Census center point of La Mesa; river miles along the main stem, rounded.
La Mesa has a cold desert climate. Summer afternoons average 96° in June; winter nights fall to about 30° in January. About 9 inches of rain fall in a normal year, with about 1 inch of snow.
On November 14 La Mesa normally reaches 68° and falls to 37°. The record high is 82°, in 1899; the record low 16°, in 1929. The most rain on this date, 0.86 in, fell in 1968.
Normals 1991–2020 and records since 1892 at State University, 11 miles north-northwest. NOAA, through RCC-ACIS.
