I have Dombeya burgessiae with pink flowers from Botanical garden, Encinitas. They look very different and almost out of bloom. This tree with white flowers is in Balboa park in Desert garden or near, I don't know borders
Dombeya is a large and moderately diverse genus from Africa and Madagascar, and a large proportion of the species have white flowers. I think if you compare the leaves with pictures of D. rotundifolia (a southern African sp.) you will see they are a good match. If you do a Google image search, ignore most of the results after about the first 15. I find the image searches return pictures with both words then follow with pictures under either word, i.e. "Dombeya" or "rotundifolia" in this case.
You also get misidentified images as well. Final determinations may require use of serious descriptions in many instances.