Even if a US Supreme Court ruling this spring makes same-sex marriage the law of the land, it would leave pockets of the country where it isn't likely to be recognized soon: the reservations of a handful of sovereign Native American tribes, including the two largest.

Since 2011, as the number of states recognizing such unions spiked to 37, at least six smaller tribes have revisited and let stand laws that define marriage as being between a man and a woman, according to a review of tribal records by The Associated Press. In all, tribes with a total membership approaching 1 million bar same-sex marriage. Several explicitly prohibit such unions, and some have even toughened their stances.

In December, weeks after North Carolina began issuing marriage licenses to same-sex couples, the state's Eastern Band of Cherokee Indians updated tribal law to add language preventing same-sex couples from performing marriages on tribal lands.