So much has been theorised and published about some “unknown” event that happened in some “unknown” time to cause California to change from an island into a peninsular.

What event? What time?

Well – we can narrow down the dates a bit and search google for a Catastrophic Californian Calamity. And then search for another one to reset the theorised reset, mud flood.

The image above is from 1752.

The one below is from 1865.

But in 1606 – California is a peninsular.

By these few images we can say that, in the 17th century, cartographers knew it was attached to the mainland. But even as late as the end of the 19th, it had become an island.

Ergo – sometime in the 20th century a mud flood or catastrophe was reversed.

Someone with more time than me can tighten these dates up.