[lentulusgracchus]

You're right that Spanish and Mexican money (and English money) were legal tender in the States for a while, but eventually Congress overreached that state of affairs at some point in the 19th century, and now U.S. legal tender is the only lawful money. Although you can barter for anything.

Without getting into the whole Federal Reserve thing .....

[ml/nj]

now U.S. legal tender is the only lawful money

You really should just lurk and not post comments about stuff you don't know much about. FRN's used to carry this notice (until the mid 1960's):

THIS NOTE IS LEGAL TENDER FOR ALL DEBTS
PUBLIC AND PRIVATE AND IS REDEEMABLE IN
LAWFUL MONEY AT THE UNITED STATES TREASURY
OR AT ANY FEDERAL RESERVE BANK.

(FRNs before 1933, weren't legal tender, but were redeemable in gold or "lawful money.") So obviously FRNs were not "lawful money" and they still aren't.

ML/NJ