In the April 1-7 1973 TV Book, this movie description is the very first listing, for 5am on the non-existent channel 53:
*** THE CLAM THAT ATE PITTSBURGH (Fantasy, 1969).
An immense bivalve mollusk goes berserk after drinking the Monongahela River and criminally assaults Three Rivers Stadium before being turned into stone by Mr. Rogers, who has a magic horseradish. Interesting, if you check the calendar. Dubbed. Sonny Tufts, Martin Koslek, George Zucco, Lionel Atwill, Wild Bill Elliot, Sabu, Mark Damon, Iron Eyes Cody, Zasu Pitts and the entire Pirates bullpen. (2 hrs.)