Foghorn Outdoors: California Hiking - By Tom Stienstra and Anne Marie Brown. One of the most useful books we've ever purchased. We've found our favorite Bay Area dayhikes from this book.

Best Easy Day Hikes - Denver (FalconGuide) - A safe bet and very cheap ($6.25). There are great rocks and open spaces in the foothills west of Denver. A book like this will help you choose.