Ryan,
There should have been someone there on that ride that should have been the ride leader. If it is a Club, they have a responsibility to help new members of the ride. Safety of the ride should be talked too, as well as Pace and the Drop-No Drop policy if applicable.
I sometimes ride with my Shop on the Tuesday Night Urban Assault ride through the city. The pace is usually pretty brisk and skills are taught during the ride. The Ride Leader always gives a brief as to the what and why of the ride. Asks about any new riders, and then finishes by counting off. All the riders should remember their number, and at various stops along the way you count back off to ensure you have everyone. If someone leaves, they let either the leader or someone near their number know that they are leaving.
The first one I went on I left early due to bonking and being unprepared. My Fault to be sure. The ride back to my car was lonely, but the ride offered to have someone ride back with me.
It helps to know the level of fitness and the speeds that the group wants to ride at. Sounds like this group is taking this more as a training ride than a ride along the greenway. It's a shame that they do this and miss out on the beauty along the way.
Keep asking around in town and see what you can find.