Sixty years predates the "city" so that includes the ten years the Herschend family operated the cave only. I am guessing that this plaque goes back to the 50th anniversary year celebrations, but I don't know why no one had mentioned it before. I will say this, maybe it was previously in another location. I noticed the Marvel Cave Plaque that used to be attached to the wall outside the Ozark Marketplace, viewable by those going into the park, in recent years was on the cave side of the pathway just outside the Hospitality House. I know some of the other employee recongition signs have been moved around in years past, too.