In north-central New Mexico lies the state’s smallest county, just 8 miles wide and 13 miles long. Los Alamos sits on a high, gently sloping plateau, cut by a series of steep, finger-like canyons. Early archaeologist Edgar Lee Hewett named the plateau “pajarito,” which means little bird in Spanish.
The county is bordered by the Jemez Mountains on the west and a labyrinth of 700- to 1,000-foot cliffs flanking the Rio Grande on the southeast. Elevations range from 5,400 feet at the river to 10,500 feet at the top of Caballo Mountain.
Volcanic activity sculpted much of the landscape of Los Alamos. Volcanic vents along the Rio Grande rift, a large crack in the earth’s crust, allowed lava to flow out like molasses and harden to form a level plain of black basalt. Meanwhile, the Jemez volcanic field to the west continued to grow, and the amount of gas-charged molten rock stored at shallow depths increased. Finally, the pressure mounted and explosive eruptions of silica-rich ash and pumice blew over a much of the United States. The overlying dome of the volcano collapsed, forming what is today the Valles Caldera National Preserve, while the local ashflows solidified to create the orange and buff cliffs of volcanic tuff that make up Los Alamos.
Because the plateau lies over 6,000 feet in elevation, temperatures rarely exceed 90 degrees. However, temperatures in White Rock Canyon, with its tumble of black basalt, can soar much over that of the surrounding highlands. Lightning storms are common during the summer “monsoon” season. Average yearly precipitation is about 19 inches while the average winter snowfall is 14 in town and over 100 inches a year on Pajarito Mountain, the local ski hill.
For more information on the natural history of Los Alamos, please see our publications, such as Los Alamos Outdoors by Dorothy Hoard.