The semi-arid or steppe climate zone encompasses much
of the San Joaquin Valley and the fringes of the Mojave Desert. Rainfall
here is less and temperatures are generally warmer than in the Mediterranean
zone. A cooler version occurs in a narrow coastal strip from Los
Angeles to San Diego.
Notable for its sunny summers, pleasant winters, and
little rain, this and the Mediterranean climate zone are what best
qualify California for inclusion in the nation's booming "Sunbelt." The
air pollution that has plagued the region in the twentieth century--casting
a noxious pall over sunny California--is the result of a sunlight-activated
chemical reaction among pollutants trapped by a combination of onshore
winds, interior mountains, and temperature inversions (in which cooler
marine air is trapped beneath warmer air above.)
The semi-arid or steppe climate zone encompasses much
of the San Joaquin Valley and the fringes of the Mojave Desert. Rainfall
here is less and temperatures are generally warmer than in the Mediterranean
zone. A cooler version occurs in a narrow coastal strip from Los
Angeles to San Diego.