(This is a comment on the blog above.)
In the mid-1970s I was living with Carole Rae an artist who felt something should be done with all the Christmas trees that were thrown out on the streets of San Francisco after Christmas. So I rented a large van, filled it with 40 trees, phoned all of our friends for a Saturday night bonfire on the beach at the Great Highway. About 50 people came to the first one, more to the one we held in the second year and still more to the third year. After that, burning Christmas trees became a tradition in San Francisco with dozens, then hundreds of people, who now fill the beach in the first weekends of January with small Christmas tree bonfire parties.
I did two things to create that incipient vital institution that later became Burning Man. First, I didn't pick an event date until the morning of the event. That made sure the wind was subdued for safety reasons. Secondly, I made sure the bonfire was as big as humans could make it. Both elements made the event fun for the kind of spontaneous people I knew it would attract.
The image of a bonfire on the San Francisco beach built with Christmas trees was new to me. However, I had seen bonfires in Kyoto the previous August, part of the Obon rituals, so I knew the emotional power of a bonfire.
What the Run with the Bulls evolves into is unknowable as were the beach fires.
A little off point diversion. Isn't it curious that bonfires have been connected to Obon for several thousand years in Japan but our etymological dictionaries try to connect bonfires to cemetery bone fires in Europe. A bone fire could never have been a bonfire, bones hardly burn. Etymologists just have a bias against the migration of words from anywhere but Europe, as I see it.