Lee,
Your friend was telling you that there are two
photo postcards that circulated through the mails in the movie.
The first one from Jack, is a photo card and features a photo of El Capitan and Signal Peak (New Mexico and Texas) NOT Yosemite (which is in California)
Possible source of confusion: There is another peak called El Capitan which is in Yosemite, and it can be photographed with the Yosemite Half Dome.
Link But this is not the El Capitan from the postcard.
the return card from Ennis to Jack, is NOT a photo card.
the "fish should be jumping" card, This pastoral scene does not seem to have any "Half Dome" rock formation on it.
and the deceased one is NOT a photo card - we are looking at the "photo" side (the address is on the reverse side)
This card is like the other one we see Ennis sending to Jack.
By the way the Brokeback Mountain postcard was not from Yosemite either.
That card was not mailed and was purchased at Higgins' store in Riverton, south of Brokeback Mountain.