Actually we're both right. I did a little more research and found that when Nature's Wonderland first opened in 1960 it was an E-ticket. It was downgraded to "D" status in the 1970's. This waining popularity is part of what lead to its being replace by BTMRR in 1976.
Hey, that would make a great Disneyland trivia question: Which Frontierland attraction started out as a C-ticket, was remodeled into an E-ticket, then downgraded to a D-ticket and eventually replaced with another E-ticket?