You are correct about that. and that is extremely hard to say. I look at places like Walker Lake which is half salt water. There are Lithium deposits all over nevada meaning that concentrated saltwater was in the area for an incredibly long time. Potentially, if there is a lithium mine or deposit present, theorhetically there could be potentially sea water there again.

And this is also not taking into account any other dams that they could use to help fill in the area. You can make water anywhere if you know how.