I changed the wording in the front section of the Crater Lake National Park article.  The source cited calls the park the "sixth oldest", whereas this article said the park was "the sixth to be designated".  These two terms are clearly different.  See this NPS timeline , which shows that Mackinac NP and General Grant NP were established as national parks before Crater Lake.  These two parks no longer exist (General Grant was absorbed into Sequoia NP, while Mackinac was simply abolished).  It therefore seemed safer to talk about Crater Lake NP's rank in age, rather than try to sort out order of establishment.