We saw this last night. As far as we can tell, that monster branch just cracked right off from the tree above. What knocked it off? Unlike some places, we're not suffering from high winds right now. Whatever the cause, we're just glad we weren't in that crosswalk when it came down.

Bonus question: where was this? SFist readers, this context-less nighttime photo might be the hardest "locate it" in SFist history...take a guess in the comments!