"California & Nevada", ISBN 0-86442-644-5 This guide gives excellent and mostly up-to-date information, rather more than you need.
"Southwest" (Utah, Arizona, New Mexico), ISBN 1-86450-376-9 This guide gives mostly great information, the desert area in southwestern Arizona could be
of more detail.
National Geographic Society: "Guide to the National Parks of the United States" This guide is excellent to prepare your trip while you're still at home. Whenever you enter
a national park you get more actual information at the visitor center.