Reddit mentions of Geology Underfoot in Southern California

I would get her some good geologic maps (in poster size) to put on the wall. Since you are in California I would recommend this one from the CGS. Additionally, the North American Tapestry of Time and Terrain is a beautiful map that you can order from the GSA. In my opinion, the best global geologic map is the GCMW which you can order here.

The great thing about geologic maps is that they are loaded with information and you can study them for hours on end. If your daughter is really interested in geology she can teach herself a lot by looking at maps, asking questions (e.g. why is there a bend in this mountain range), and then researching that question. Even just studying the legends on the maps is useful since it will give her an idea of what kinds of rock are typically found together.

Also, pick up a copy of Geology Underfoot in Southern California.