This book is coming so close to DNF'd. If I weren't trying to win a bet, I'd have tossed it by now.
For two states now, Arizona and Colorado, the author has been hinting that the lack of wilderness related disappearances in the thirty years between the early fifties and the early eighties is part of some bigger plot. The pre-50s disappearances all involve people around the same age, whereas anything goes in the post-80s period.
Gee, there couldn't possibly be any cultural, economic, or technological shifts in post-WWII/pre-80s America that could explain why people didn't leave the house as much as they used to, especially in the wild on their own. Like television. Or the rise of summer camps. Similarly, it's not like huge swathes of Americans were enlisted or drafted at various points in the timeline, thus skewing the age demographics of national park/forest/wilderness visitors. It's a complete mystery how the Wonderbread generation just didn't wander off in the same way the post-hippie and "save the forests!!" crowd did, for that matter.
Nope, apparently there's totes some sort of predator involved. Guess he or she didn't feel like ambushing innocent berry-pickers for thirty years. Screw this book.