LOS ANGELES  —  The wildfires burning across Southern California (search) draw much of their strength from the fiercely hot and dry winds known as the Santa Anas (search).

Santa Ana winds are formed when a high pressure area forms over the Great Basin (search), the vast expanse of desert that covers much of Nevada, Utah and southern Idaho.

That forces cool, dry desert air toward the southwest. There, the winds plunge down through the mountains of Southern California, channeled by steep terrain toward areas of comparatively lower pressure.

As the winds whistle through canyons and valleys of the mountains that separate the desert from the coastal strip between San Diego and Santa Barbara, the air is compressed and heated as it descends, sometimes dramatically. The winds also pick up speed as they travel toward the coast.

The winds dry out vegetation and sap the air of humidity, creating the potential for destructive fires.

If a fire does break out, the Santa Anas only further fan the flames. Gusts of up to 70 mph are not uncommon.

The Santa Ana winds typically blow between September and February.

The winds were named by settlers in the area of Santa Ana, a city 40 miles southeast of Los Angeles.