OK, what I gather from the training diary of Michael Williams is that from the beginning the ride was associated with the word "fast." We also get a date for the naming of the ride on June 7th.
Michael Williams, Training Diary- 1976
(I was a second year junior) which is a Taco Bell calendar
First note of a river ride is:
May 18th, 1976. I have notes earlier in the calendar on Tuesdays and Thursdays of that May riding with a particular rider (Bobby Edwards) who I believe started the ride as a regular event. May 18th it was just two of us.
May 25th there were four of us.
June 1 and 3 notes "Freeport. Fast."
June 7 I noted it was the "River Ride" for the first time. Before that it was "ride to Freeport", etc. from there after in the year the RR shows up every Tuesday or Thursday that I was in town and not injured
October 7th. Last River Ride of that year
Early riders on the river rides were Bobby Edwards, Greg Edwards (still riding), Steve Uhler (also still riding), Mike Fitzwater (one of Jess' original partners), Tom Bartlett (also one of Jess' original partners and who hired Steve Rex to wrench in his shop BiciSport), Phillip Muller and probably Jess P as well.
Thanks for the information Michael!