Description: my friend and i were driving around (i was driving)on Glorietta Blvd. in the evening; I'm not sure what time exactly but it was after dark and as it was over forty years ago, the day & month and year may be wrong.

As we drove along as teenagers do  we noticed a bright glow that appeared to come from the back of a home on that street.  This is a ( or was at the time)a semi-rural area; now more filled in. 
As we drove slowly by the light silently rose from the yard and we followed it out Glorietta Blvd.  This street runs south to north and drops off abruptly into the valley in which' if you follow it in an easterly direction, goes through Lafayette and out past Walnut Creek towards Mt. Diablo.  
The light went north above Glorietta Blvd and when the road dropped down to the valley it headed east towards Mt Diablo and at an amazingly fast rate and disappeared (or rather we saw it fly ) on past Mt. Diablo. 
I will never forget it and absolutely no-one I told about the incident would believe me,but I know it was not from our neck of the woods.  
Not much of a story but there has never been a moment in my life since that I have doubted the existence of intelligent life beyond our recognition or comprehension.
Source of report indicates that the date of the incident is approximate.  PD