It appears, to me, that it would be SEPARATE from California.
The meaning is: "...no new State shall be formed or erected within what had previously been the jurisdiction of any other State..."
In other words: No new State may be formed on territory hitherto within the jurisdiction of any other State.
Regards,
When the state of California goes bankrupt and is forced to revert to territorial status, there will be a opportunity to admit parts of it as separate states - provided that they can demonstrate fiscal solvency.
“In other words: No new State may be formed on territory hitherto within the jurisdiction of any other State.” . . .”without the Consent of the Legislatures of the States concerned as well as of the Congress”
Appears it can happen but needs approval at all levels.
Any ‘meaning’ is parsed by the legislature.
The ‘words’ are quite plain.