Its an annual event put on to support the Boys Republic of Chino, CA. Steve was sixteen when he went to the Boys Republic in 1946 and never forgot the place. It is a non-profit, non-sectarian community for at risk boys and girls ages 13 to 17.
Arnold Welch was there with his restored Bullitt Charger. This is the one that he found had been one of the two actual Dodge Chargers used to film Bullitt. Here are some photos provided by Arnold:
And here is a link to a video of to vast sea of Bullitt Mustangs that were there: