The current guidebook Climb El Potrero Chico by Pancho Villa and the Caguama Queen is now in its 11th edition and available locally for $12 (look for Magic Ed's green station wagon). With new route development continuing at a stout pace, it is now the only up-to-date guidebook. Crisp, to the point, and reasonably accurate. Now long out of print, the older Mexico Rock by Jeff Jackson is of historical interest and also contains some valuable information on other nearby and not-so-nearby Mexican climbing areas.