IOW, California can't do this?
I dont know
The actual clause is: No State ... shall make any Thing but gold and Silver Coin a Tender in Payment of Debts" There is NOTHING there about "United States money." In fact in Thayer vs. Hedges 22 Ind. 282, 286-87 (1864) the court said: "States, though they cannot coin money, can declare gold or silver coin or both whether coined by the Federal, or the Mexican, or the Spanish Government shall be legal tender." Thayer also said, "The words delegating to Congress the power 'to coin money,' regulate the value thereof and 'of foreign coin' do not include the right (sic.) to coin money out of paper."
We've come a long way, baby.
ML/NJ