Location of the Roman frontier wall, Limes, in the German state of Baden-Würtemberg https://www.liz-bw.de/limes-baden-württemberg/
https://files.mastodon.social/media_attachments/files/111/077/533/778/867/785/original/425abce735d14211.jpg
Now this comes as a surprise, do you have any special ties to Stuttgart and Baden-Württemberg?
Though, IDK, the weather there is anything but California. And there are not even enough lakes, leave a lone an ocean.
(And no, Lake Constance doesn't count. It is not the Swabian Sea. That is just some PR trick.)
Oh, and car manufacturing is much more professional there than in CA.
In any case, regarding that southern wall, I suggest resurrecting the Roman Limes:
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