@ Calgarian (post 632):
From my scrutiny of the postcard shot in the post which preceded yours, I'd say you were close with your guess of "late 60's", but I'd place it a little later...maybe mid 70's.
In the Petrigo postcard I can make out the Palliser One, Royal Bank, Pacific 66, Standard Life, Norcen, and the Place Concorde towers. Only the Royal Bank was up by the close of the 1960's. The rest of them were built between 1970 and 1975.
However, I don't see Shell, nor the Home and Dome towers, all of which went up in 1977 or so.
For that reason I'd place the date of the shot in 1975, which was the centenary of Calgary's founding (and that may be the reason Petrigo took the photo from where he did in order to place the Fort Calgary site in the foreground).
Even if only in the period spanning my own lifetime, Calgary, you've come a long way, baby!
HT