Lori ...
There are a lot of roses that will scramble up trees.
The first photo in this link is a bansia rose in the Sacramento Historical Rose Garden
http://www.cemeteryrose.org/ar...
Here are some photos in the ATP database of R. banksia lutea
Lady Banks Yellow (Rosa banksiae 'Lutea')
Any of the bansias will climb and cover trees like this and can handle heat are drought tolerant.
'New Dawn' is often suggested for this purpose, but I suggest you shy away from that rose because it does not like the central or southern California climates.
