Two kinds of cases make up almost a third of a;; in our history. They are: states suing states over the allocation of water from the Colorado River, and states suing states over the legal residence of Howard Hughes (and therefore the state estate taxes) at the time of his death.
This is NOT an original case. It is like the twelve or so cases that I took to the Supreme Court challenging state election laws. All of them began at the trial level, and in due course reached the Supreme Court.
John / Billybob