David, I know my wife has looked at the link you sent but I've only had time for a quick scan. What I saw looks interesting and I must find time to have a closer scrutiny.
Some years ago we grew a few Ceanothus from seed. They didn't survive, probably due to the fact that we watered them in hindsight, but as they grew well in UK with their wet summers I hadn't taken that into account.
As for the Fremontodendron, we haven't tried one here but I remember there being a large one growing against a wall at Capel Manor in Enfield, North London, and that coped well with English summer rain. Again, probably for the same reason you mention regarding the ceanothus.