Actually, the date they all went to Joshua Tree was in the Fall of 1968.
My author friend, David Meyer, wrote the best bio on Gram titled "Twenty-Thousand Roads." A lot of sites and people think that Keith and Anita flew out to visit Gram in 1969, but she would have just had Marlon, and her hair would have been longer and darker. In the Joshua Tree photos, she had just finished filming Performance and her hair was short and dark blonde (not her usual platinum as she wore it in 1966 and 1967). I think she looks very pretty and healthy on the Joshua Tree shots.