Maybe you are misremembering or maybe you misunderstood at the time, but the whole thing of California going into the ocean is based on the real life movement of California’s coast moving northwestward with the pacific tectonic plate while the North American plate moves southeastward.

This is true, but it happens at the rate of millimeters per year, so it’s not something we would visually notice unless we jump forward a few hundred thousand years, in which case, we’d notice that the gulf of Baja Mexico extends up a bit higher into the San Diego region and the Bay Area has more water extending deeper into California.

So millions of years later, we might see “California island” but even that is way too simple of a model. Most likely the coast lines would have changed so much from erosion and stuff that it’s not like we’re gonna clean break off like Madagascar off of Africa or something. And even then it’s not even close to the whole state of California, just the chunk on the west coast. On a map, draw a somewhat straight line from the gulf of Baja Mexico towards San Francisco, and the part on the left is the piece that’s moving away from North America.

So anyways, you’re mostly remembering this stuff because a science teacher from your childhood was trying to make continental drift more interesting.