I'm not sure how it works in the States, but over here most of the "fun rides" of 100km, and 150km have several sections - most of the entrants are casual riders, but the ones that want to race it are started first... with people having to place themselves in time-zone starts of how long they think they will take to finish the course.

This is for safety reasons so the very fast riders don't take risks trying to pass slower riders and so forth...

There is often a prize money category but you have to provide evidence of a qualifying time for that.

The best way to find out is to ask the organisers.