The Rope, by Nevada Barr

This is a prequel to the series, and takes place in Glen Canyon where Anna has gone to try to escape after the death of her husband. Then she gets sort-of kidnapped and trapped for a couple of days in a deep hole in the desert. Creepy--had a little bit of trouble with the idea of her being at all willing to going underground in Carlsbad Caverns (in a later-in-life book written about 10 years ago, which cured me of EVER doing any spelunking!).

Anyway, this is how Anne ends up as a Park Ranger. Not sure how effective it is in explaining that, but it's wonderful to find out a bit more about what she was like as a young, pretty woman. A redhead? Who knew? :-)