In this book, McPhee teams up with a Geology professor to explore what is known as the Basin and Range (the greater Colorado area). He talks about his exploration into the theory behind the unusual formations in the area and adds a bit of intrigue as we learn that the professor is also interested in finding old silver mines and reprocessing the discarded ore to find left behind silver (and he does). In general, this book provides a fascinating insight into a very geologically unique area of the world.
Interesting tidbit: while sand stone and silt stone look very similar to the unaided eye, sand stone is gritty when chewed on while the silt stone is creamy.
(Annals of the Former World is a collection of five different books about geology written by McPhee).