In an unprecedented move, Golden Gate Bridge northbound lanes will be closed Sunday due to terrorism concerns during SF marathon. (This will affect hundreds of thousands, it is the only route north out of SF.) [Golden Gate Bridge to close partly Sunday for SF Marathon out of terror concerns, By Mark Prado, Marin Independent Journal, July 21, 2017]
Most news coverage does not mention terrorism concerns, but the obvious reasons for this caution are the Boston Marathon attack (committed by Chechen Muslim immigrants) and truck attacks like the one in Nice (committed by a Tunisian Muslim immigrant.)
While this is going on, the idiot 9th Circuit Court (in SF), California Governor Jerry Brown, California AG Xavier Becerra, Congresswoman Nancy Pelosi, and Senators Dianne Feinstein and Kamala Harris all support open borders.
See earlier letters from the same reader.