You would have to prune the rose back quite a bit to make sure that the
move goes smoothly, which of course means that you won't be seeing any
buds for quite some time. Generally, you don't want to leave more
above-ground growth than the root can adequately support, and that would
require that you prune back severely.

Theoretically speaking, you can move the rose any time the ground is
workable, so you could do it now and get away with it if you take care
to get as big a rootball as possible, and pay special attention to its
needs. To ensure that everything will go swimmingly, I would wait until
the temperatures cool off again, probably some time in the fall or early
next spring. I don't know if the roses have a dormancy period in CA,
but if they do, the best time to move them would be before they
completely break out of it (buds are starting to swell, but no leaves
yet). Even then, you will still have to cut the canes way back, but the
rose is likely to recover rather quickly from it.

Thanks Suja. I may try and transplanted it, taking care to get a
large rootball. If things *don't* go smoothly, what should I look for
as signs that it needs to be pruned back more than I did? Will it
wilt or turn brown or drop leaves?

Thanks for your advice.

-F