From Critical Mass: Critical Mass is a mass bicycle ride that takes place on the last Friday of each month in cities around the world. Everyone is invited! No one is in charge! Bring your bike! Next San Francisco Critical Mass: April 26th, 2013, 5:30pm, at Justin Herman Plaza (foot of Market Street).

From SF Critical Mass: Critical Mass is a mass bicycle ride that takes place on the last Friday of each month in cities around the world. Everyone is invited! No one is in charge! Bring your bike! Next San Francisco Critical Mass: May 31st, 2013, 5:30pm, at Justin Herman Plaza (foot of Market Street).

From SF Critical Mass Website: Critical Mass is a mass bicycle ride that takes place on the last Friday of each month in cities around the world. Everyone is invited! No one is in charge! Bring your bike!

Critical Mass is a mass bicycle ride that takes place on the last Friday of each month in cities around the world. Everyone is invited! No one is in charge! Bring your bike! From Critical Mass

Critical Mass website.

Critical Mass is a mass bicycle ride that takes place on the last Friday of each month in cities around the world. Everyone is invited! No one is in charge! Bring your bike!