What spare time?
California Trolley and Railroad Corporation - CTRC - http://www.ctrc.org/ - CTRC restores and preserves railroad equipment as it was used to serve the people in Santa Clara Valley, California. CTRC is a 501(c)(3) non-profit California Corporation. I have been a member for a number of years and have occasionally (far too occasionally) been seen helping with the restoration of a 1923 mainline steam locomotive.
TheatreWorks - http://www.theatreworks.org/ - TheatreWorks is one of Northern California's five largest theatre companies. I have worked as a crew member (usually on lighting) on dozens of productions over the last ten years.