Try doing an amazon search for Michael R. Kelsey:
http://www.amazon.com/s/ref=nb_sb_noss_1?url=search-alias%3Daps&field-keywords=michael%20r.%20kelsey&sprefix=michael+r.+ke%2Caps&rh=i%3Aaps%2Ck%3Amichael%20r.%20kelsey
He has written some extraordinarily interesting and dense guides to areas in the Colorado Plateau. For a long time I have been telling people this is how guides should be written. Unfortunately, to find people capable of writing them this way is probably very difficult. Personally I enjoy reading them just for all the information, even if I don't go to a particular spot. Details on routes and ideas for places to go – yes. But also archeology, geology, history, natural history…etc. The are not coffee table books. There are loads of picture, but instead of glossy color photos of some stereotypical spot you are more like to get tons of B&W historical picture. In short stuff that has dept.
I have the Canyonlands NP, Green River Guide, and the one on the Henry Mountains. Get one and check it out, and if you like the style you will be all set for any areas he has covered.
Unfortunately no book specifically on Zion, unless he has some of those those trips in his non-technical canyons book. But for SE Utah he is awesome.