Email From:Garlyn H.-San Mateo, CA (near the College of San Mateo)
I was sitting in the backyard reading a book by red headlamp when a white/blue light flashed across the sky (apparently from a SE to NW direction). I had enough time to think "Oooh lig... [lightning] " when a sound like a big explosion occurred. Family in the house heard the noise, as well as across the street neighbor and his son who was in his vehicle exiting highway 92 at West Hillsdale exit.
Looking in southernly direction afterward was unable to see anything suspicious or alarming. No fires. No areas of blackouts. Air traffic into SFO continued and appeared uninterrupted ( NE of my location)
Regarding time & date of event:
I sent myself a text on 10/21/2011 at 2123 stating " flash & explosion. 2 min ago?"
Hope this helps.