I was wondering if the legal codes in states (like New Mexico), that used to be part of the Spanish empire, retain some of the old laws from those days?
Not quite what you were looking for but Louisiana is the only state with a fundamentally different legal system than the other 49.
“Louisiana’s civil code has kept its Roman roots and some of its aspects feature influences by the Napoleonic Code, but is based more on Roman and Spanish civil traditions. As a result, the bar exam and legal standards of practice in Louisiana are significantly different from other states, and reciprocity for lawyers from other states is not available.”
That brings up an interesting question. Where did the states get their laws from when they were new (oh crap! we left out second degree murder.)? It seems like a lot of work to just create all laws at about the same time but maybe that is what they did.
Most of the US got its legal system from England, a system called the Common Law which is a mixed system of statutes and judge-made law/precedent (vs Civil Codes for which precendent is unimportant).
In modern times, something called the Model Penal Code, which sets out a “model” system of criminal law according to certain philosophical principles, has influenced many states in forming their laws. Unlike the UCC though, its not a set of legislation you have to sign on to, but just a guide from which states can pick what they like and leave the rest (some states, like NY follow it quite closely)
In theory, the old land grants are still valid. Part of the treaty of Guadelupe Hidalgo was that the US would uphold all old land grants, though the Senate ratified a version of the treaty without that provision. There are still lawsuits over it.
As far as I know, that’s it for New Mexico.
New Mexico was part of Mexico after it was part of Spain, so you have another step in between.
Of current parts of the U.S., it’s only Florida that has a significant chunk that went directly from Spain to the U.S.
In the case of the original colonies, they just continued with the tradition of English common law and whatever statutes and royal decrees were in place at the time, except where those violated the new Constitution. A recent case concerning fishermen’s rights on Long Island involves the interpretation of a royal decree called the Dongan Patent which was written in 1686, for example.