The Sierra Club Guide to the National Parks of the Rocky Mountains and the Great Plains

We took several guide books with us when we took the Great American Vacation last year, but this was the one we returned to again and again. The sections on each park were big enough to give you plenty of ideas for things to do during a 3-4 day visit, but not so big as to be overwhelming. It has a nice introductory section for each park, a list of hikes of various difficulties, good maps and beautiful pictures. You won't need a separate guide for each park if you have this book.