From Day Of The Tread event info:

Whichever path you choose, all participants enjoy a Sunday pre-event motivation gathering, a post-ride celebration, courses full of music, entertainment, themed recharge zones and crazy contests. Costumes are encouraged but not required; we will be awarding prizes for the best human costumes and best bike costumes. So! If you like dressing up in costume, putting on face paint or wigs, come join us as your favorite witch, ghost, goblin or monster. Participation ensures a ghoulish-good time!
Come join the fun and show your support for the Carrie Tingley Hospital Foundation and Casa Esperanza.

Here’s a little video of that day!