I have not read the book, but I have lots of experience with search and rescue operations, primarily in southern Arizona, 1958-1985.  Obviously, you increase the odds when you solo, but who doesn't, at least occasionally?  I certainly have!

Navigation is a critical skill, and even then, with lots of experience, you can become "confused" now and then -experience speaking...

There is nothing about National Park Service areas which makes them inherently more or less safe that any other wildlands.  Staff capability varies tremendously.  A good many parks rely upon outside groups when extensive SAR is required.  That is frequently a very satisfactory arrangement with good outcomes, but recovery is rarely rapid.  Self sufficiency is always a good idea, even on well travelled trails.

Sometimes, even that is not enough.  Consider the case of Paul Fugate, a NPS Naturalist who left the visitor center to check the nature trail in January, 1981, and hasn't been seen since, despite an extensive SAR that went full blown for two weeks, and continued with specialized operations for months afterward.  The case is still open and unresolved....

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