In researching the Juneau, I discovered the image below, which was taken on July 1, 1951; just a few days before the parade seen above. Notice that the whole crew is out on the deck in their whites. I also discovered a short historical document about one of the crewmembers, Vern Meemken, who is more than likely one of the sailors marching in the parade.
The photo below is another scene from the 1951 H.B. 4th of July Parade. This time, it's the local Boy Scouts and Cub Scouts. You can tell it was still very much a hometown parade.
Although this annual event is now one of the largest in the country and is often televised, "people-dumped-onto-a-flatbed-truck" continues to be a popular theme for parade entries. At least they're better than the units where kids (from other cities) walk down the street while someone carries a blaring "boom box" behind them. Oy.
However you end up celebrating, have a great Independence Day.