As noted above, much of Louisiana law is derived from the Napoleonic Code; the adherence to French legal traditions stems from its time as a French colony. Puerto Rico is also a civil law jurisdiction of the United States. However, the criminal law of both jurisdictions has been necessarily modified by common law influences and the supremacy of the federal Constitution.
Many states in the southwest that were originally Mexican territory have inherited several unique features from the civil law that governed when they were part of Mexico. These states include Arizona, California, Nevada, New Mexico, and Texas. For example, these states all have a community property system for the property of married persons (Idaho, Washington, and Wisconsin have also adopted community property systems, but they did not inherit them from a previous civil law system that governed the state). Another example of civil law influence in these states can be seen in the California Civil Code, where the law of contracts is treated as part of the law of obligations (though the rules actually codified are clearly derived from the common law).
Many of the western states, including California, Colorado, New Mexico, and Wyoming use a system of allocating water rights known as the prior appropriation doctrine, which is derived from Spanish civil law. It should be noted that each state has modified the doctrine to suit its own internal conditions and needs.