From EBBC:

The Ride of Silence is a World-wide event held the 3rd Wednesday of each May (since 2003). The intent of this event is to show respect for cyclists who have been killed (including my friend John Greaves, Camino Tassajara – June 2009) or injured in vehicle collisions, support Daneil Greaves (his widow) who is the local contact for the ride (2nd year) and raise awareness that cyclists have a legal right to the public roadways.

Wed., 18May starting at 7:00 pm.
Starting location Arbolado Park, Walnut Creek
3341 Arbolado Drive, Walnut Creek

The Ride Of Silence is a free ride that asks its cyclists to ride no faster than 12 mph and remain silent during the ride. There is no brochure, no sponsors and no registration fees. Although, I occasionally dabble with mountain biking, I’m not a road cyclist. However, for this worthy event I will once again make an exception and participate. It’s an easy ride, folks ride road or mountain bikes and the pace is intentionally slow and everybody is kept together!

Cut and paste the following links:
http://www.rideofsilence.org/main.php
http://www.rideofsilence.org/locations-domestic.php?s=CA#CA
http://www.ktvu.com/news/23615503/detail.html (News Coverage from 19May2010)