Unlike some of Stratton-Porter's other charming fiction, this is blatantly racist and anti-Japanese. It was a shock for me to read this as a kid after having read Girl of the Limberlost.
I will warn you now: this is NOT "Girl of the Limberlost". I wish Gene Stratton-Porter had never come to California or set one of her stories there. Her beautiful descriptions of unspoiled land around Los Angeles are ruined by very shallow characterization, and racism as poisonous as Hitler's. This book stayed out of print and off shelves for good reason. If you are a Stratton-Porter collector or accustomed to reading shocking viewpoints of that period, have at it. Most readers will be insulted.
This survival adventure switches back and forth between the Stone Age and the present day (the 1980s). If you're interested in prehistoric man, archeology or spelunking, you'll be fascinated. Much effort was made to flesh out the characters of the modern-day cave explorers. However, the most memorable and haunting passages are those set during the prehistoric people's ordeal.