Fiona is correct, it was the pouring of the first concrete to create the caissons for the Skye bridge, which were floated to the site and support the road bridge.
As I recall Ian MacLean's daughter was the youngest person working on site, so was called upon to initiate the task.
Although this was done for TV & newspapers, the concrete never actually poured that day, the mix failed to meet the specfications, although little was said of that at the time.
I have perhaps the most extensive archive of video & phototgraphs regarding the Skye Bridge. It starts with an exhibition in the council offices in Portree of the various designs proposed for consideration.
Whilst people tend to remember the toll protests after the opening of the bridge, that only really started the day it opened. Prior to that there was a very active and totally separate organisation against the building of the bridge.
Perhaps the most moving footage on video for me was the final day for the ferries, when passing ships sounded their farewell on sirens. The last ferry left Kyle of Lochalsh for Skye packed with people and a pipe band. On the slipway tears rolled down some faces as they watched the end of an era.
I still retain most of those tapes but no longer have a BetaSP broadcast format video player to show them. Maybe one day I will get a scanner and at least put on line the history of the bridge in photographs.