The Santa Ana winds are basically dry air from the interior of the US blowing into the Los Angeles Basin, and generally owing their existance to an extreme low pressure system somewhere over the Pacific Ocean off the southern coast of California. These winds, at their most extreme, tend to be the cause of much grief in the way of toppled utility poles, broken utility lines, turbulence on airplanes departing from and approaching not only LAX but also SNA and ONT, and toppled trees, but are also cause to some (albeit dangerous) fun (for instance, riding along Santa Ana Canyon Road (a segment of former US Highway 91, now replaced by California Highway 91) into Orange from Anaheim Hills on a bicycle without actually pedaling).

They are also a catalyst for many brush fires that have happened in the Los Angeles Basin. Simple physics - dry brush, hot winds - and one blithering idiot with a cigarette flung out the window, and you can burn up hundreds of acres in a matter of a few hours.

The biggest cause for the insanely high wind speeds that I see is a combination of increase in speed and temperature proportionate to a decrease in altitude, coupled with the fact that the winds compress as they go through areas like Santa Ana Canyon.