I recently bought
Geological Journeys: A traveller's guide to South Africa's rocks and landforms, by Nick Norman and Gavin Whitfield. It's published by
Struik, ISBN 1-77007-062-1.
It's designed to be a companion for car journeys, and has a chapter for each of the major national routes (N1, N2, N17, N3, N4, N7, N12, N14), for major cities (Greater Joburg, Cape Town and Durban) and for tourist areas of geological interest (the Great Escarpment, KZN Drakensberg and the Little Karoo). The introduction that explains basic geological terms and concepts, and lovely photos, maps and diagrams accompany the text throughout.
The book is not specifically about SANParks, but includes geological information about many parks, including TMNP, KNP and Augrabies. The general geological information is also of relevance to those visiting parks, and will be of interest to anyone who'd like to understand the natural world around us better.
Geological Journeys is clearly written and it's a book that I'll definitely be taking in the car as drive around the country. I would really recommend this book.