The Bay Area IndyMedia web site offers this calendar where you can enter event information directly.
Action Together West provides a calendar of many Bay Area activist events.
Mobilize US has a list of events, petitions, and volunteer opportunities, with the closest events to you listed first.
Bay Resistance has a calendar of Bay Area activist events.
TeslaTakedown lets you find local protests of Elon Musk at Tesla showrooms.
The Political Revolution lets you enter a zip code to find local activist events.
The San Jose Peace & Justice Center offers this calendar.
The Peace and Justice Center of Sonoma County has an events calendar on their front page.
KPFA Radio publishes a list of events at http://kpfa.org/events/.
Occupy Oakland has a list of events.
The Planet Drum Foundation maintains a calendar at http://www.tinyurl.com/GreenCityCalendar.
Media Alliance has a calendar of events at https://media-alliance.org/bay-area-events-calendar/.
The Ecology Center in Berkeley posts an EcoCalendar at https://ecologycenter.org/calendar/. The calendar is also available by email.
One Brick posts a calendar of casual volunteer opportunites in the Bay Area. One brick adds a socializing / networking element to volunteering.
Here is Acterra's Community Calendar of environmental events (mostly on the Peninsula).
The San Francisco Bicycle Coalition posts this calendar of cycling-related events.
Also see these organizations indexed under "calendars".
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