The Zoo has a slightly different rule :
The first Wednesday of every month, admission to the Zoo is free for San Francisco residents only. Please show proof of residency through a valid driver license, identification card
The Academy of science also has free Wednesdays but it is the third, not the first Wednesday of each month. There will be no members-only entrance on free days.
In addition, SF residents can get in for free on some weekends http://www.calacademy.org/visit/plan_a_visit/sf_free_days.php
Sunny_Vale
it is always free on the first Wednesday of every month.
http://www.exploratorium.edu/visit/hours_admission.html
AFAIK other museums are free on that day too.
The Zoo has a slightly different rule :
The first Wednesday of every month, admission to the Zoo is free for San Francisco residents only. Please show proof of residency through a valid driver license, identification card
The Academy of science also has free Wednesdays but it is the third, not the first Wednesday of each month. There will be no members-only entrance on free days.
In addition, SF residents can get in for free on some weekends http://www.calacademy.org/visit/plan_a_visit/sf_free_days.php