I found an interesting selection at Google Books called The Geography of Marriage: Or, Legal Perplexities of Wedlock in the United States, published in 1889. The author notes inconsistencies in the marriage laws of various states, and expounds upon the dangers of miscegenation, of polygamy, and of living in Arizona.
A mistress or concubine up to the present time has never been accorded the rights and privileges of a wife, and it has come to be a maxim that mere concubinage can never drift into matrimony, nor become wedlock by lapse of time. This rule, however, has been reversed in Arizona, by a law passed February 28, 1887, whereby it is declared that parties who have lived together as husband and wife and continued to do so for a year, shall be considered as having been legally married; and if either die within the year the same result follows, and the children are declared legitimate. Within the geographical limits of Arizona, therefore, if nowhere else on the globe, it is possible to become husband and wife without getting married at all. [Link]According to Wikipedia, Arizona banned common-law marriages in 1913, shortly after becoming a state.