Mystery in the Cave

When the Aldens' explore Dragon's Mouth Cavern, they encounter some suspicious people.
While exploring the caves around Dragon's Mouth Cavern, a series of unusual and somewhat frightening events convinces the Alden children that someone does not want them around.

Blind Descent

Blind Descent by Nevada Barr

Forced to cope with her claustrophobia and to use all the skills she has developed above ground, park ranger Anna Pigeon enters the dangerous Lechuguilla Cavern in New Mexico's Carlsbad Cavern National Park to attempt a rescue and learns who she can trust and who can be saved.