Wingtip vortices for sure. They are a byproduct of wing (and fuselage) lift, NOTengine thrust / "displaced air" / downwash etc. (which all are ALSO hazards but nothing like wingtip vortices). They sink behind the airplane and/or drift with the wind (I think FAA says 700ft/min "normal" sink rate). They are a serious hazard even to a "heavy" airplane, for instance in taking-off behind another "heavy", a pilot has to explicitly waive the "wake turbulence" waiting period. Even light airplane can generate significant wake turbulence (one funny instance is that in certain aerobatic figures, if well executed, you end up flying through your own wake turbulence)
I think kites generate wingtip vortices too, anybody who experienced a tight racing start at Crissy can vouch to that.
I always assume that at 3rd/Coyote is too windy to hit a vortex intact. Probably you were just in the sweet spot for it (wind direction/strenght, height under approach, air stability etc.)
http://www.youtube.com/watch?v=uy0hgG2pkUs




