A few times each year in Santa Clarita, the conditions are just right for these strange clouds to form. They're sometimes called "UFO" clouds because of their rounded, saucer-like shapes and hovering behavior. In the scientific world, they're known as Lenticular clouds (Altostratus lenticularis), or "standing wave" clouds, and generally form over, downwind of, or sometimes upwind of mountain ranges.
The cause is interesting... Air (wind) moves much like water - it flows over the surface of the earth and when it encounters surface features (like mountains) it flows up and over them like boulders in a river, generating ripples/rapids in the airstream above and downwind. Lenticular clouds form when moist air from lower altitude is forced up into colder layers of the atmosphere where it condenses, usually at the peaks of the air "rapids". As the air descends down from the peak of the rapid, it warms and evaporates, the result being a cloud that remains mostly stationary while other clouds at lower altitudes (and cirrus at higher altitude) moves past it.
This basic diagram shows a bit of what's happening:
This event occured in the afternoon and evening of March 9th, 2010 and provided some spectacular skies around sunset.
Another interesting item in the sky near sunset was a jet trail fragment cross in the nearly perfect shape of an X-Files "X" - even the font was right! Two still images captured with a Casio EX-F1 at 12x zoom show this interesting feature close-up, while an annotation in the last time lapse video sequence shows it barely visible at such a wide angle.
The music is the last half of "Lunar Seas" from the "StarSpin" online CD (EP) by TECHNICIAN (yours truly), which was originally written and released (in part) on the "Fun with Fire" video. Full artist discography available at HTTP://technician.jcmdi.com
Stock footage from this video (and many other JCMDI productions) is available free, for non-profit use in your own YouTube videos from the JCMDIStockFootage channel.