<Santa Ana> winds are born of weather systems out in the Great Basin, in high-pressure zones over Nevada and Utah. The cold, dense, moist air descends from the high deserts and mountains toward the Pacific Coast. It is funneled through canyons and passes, gaining speed and heat from the land.
As it drops to sea level, it can warm by 20 or 30 degrees and becomes very dry. On Monday, temperatures near the San Diego and San Bernardino fires reached the upper nineties, and the relative humidity was less than 10 percent.
Mountains in Southern California are geologically young. They haven’t eroded much and thus have steep narrow canyons and gullies. Not only does this make getting fire trucks in a difficult task, the amount of brush and undergrowth in these areas can be stupendous.
Yesterday I hiked in about fifteen minutes on the outskirts of Topanga State Park to take photos of the Simi fire across the valley. The brush and vegetation is mostly dead and bone dry. But here’s what those who don’t live here may not know – in such areas you can’t wander off a fire road or trail because the brush is impenetrable. Such brush can easily be three feet high, and six feet high is not unusual.
Imagine thousands of acres of bone dry brush several feet high in areas so steep that walking off trail is difficult, if not dangerous. Then, imagine how fast and how furiously such areas would burn if ignited and how hard it would be to put it out.