For people interested in the subject generally I highly recommend John McPhee's anthology "Annals of the Former World." Actually I highly recommend everything John McPhee has written but this is a good start :).
I used to think geology was a dumb science, but this book single-handedly made me obsessed with the topic. Geology is really more like "earth history" and it's a startlingly young field, a dynamic which plays out across the volumes.
"may inspire circuitous road trips involving many stops dangerously examining road-cuts on busy interstate highways"
More directly related to the Green River, I found Wayne Ranney's "Carving Grand Canyon: Evidence, Theories, and Mystery" an accessible/engaging intro to deep geological mysteries.