I don't think there are any native Echeverias in California, although Dudleyas have been called Echeveria in the past. Most Echeverias are not white, and most Dudleyas are at least somewhat white unless they are thoroughly washed clean.
The real way to tell them apart is by the flower stems. Look on
this thread where I mis-identified an Echeveria. Then look at these actual Dudleya flower stalks:
![dudleya-0408.jpg](./download/file.php?id=40756&sid=9a179ebf9e2e9251f692138a8a3f900b)
- dudleya-0408.jpg (83.46 KiB) Viewed 1637 times
The flowers themselves are similar, but the stalks are highly branched with the flowers standing up instead of an unbranched gracefully curving stem.