I found this long but very interesting thread about the pictograph rock in Blair valley.
http://www.humancafe.com/cgi-bin/discus/show.cgi?tpc=6&post=725#POST725It may take you awhile to read thru all of it and it's links but I found it very interesting and made me think more about some of the things I have seen and photographed in Anza Borrego. It also has spurred some more interest in exploring the desert and trying to find out more about the Kumeyaay who lived there so long ago.
Daren