Florida, Texas, and California all belonged to Spain but had small populations when the Americans from the US began to flood those places, and the political institutions and legal institutions were imported from the older states of the US, going back to the English experience and English common law. I don't know about New Mexico--it could be a partial exception since there was a larger Spanish population there in 1848.
The Louisiana Purchase territory had been under Spanish rule for about 40 years but I think the traditions there were mostly French.
I think Lousiana is the only State that doesn’t base their legal system on English Common Law.