The tradition started in 1979 when a man celebrating his birthday bet the patrons in Mugs Away Bar that he'd buy a drink for anyone who went out across the street and 'mooned' the train when it passed by.
In 2002 I started riding with a fundraising group, we had training rides and did a couple of organized bicycling rides. That year I read about the Moon Amtrak tradition in the LA times and decided I would put a training ride together the following year.
Now 15 years later it has become a ride that people do every year. It's a way for me to keep in touch with the friends I made biking and also to continue to fundraise.
You probably won't find an event like this anywhere else!