In defending Nevada's ban on gay marriage, the administration of Governor Brian Sandoval, a Republican, argues that the ban is rooted in history and “not based on policy whimsy.”

In 2012, U.S. District Judge Robert Jones upheld the state's ban, writing that the U.S. Constitution's guarantee of equal protection does not prohibit “the People of the State of Nevada from maintaining statutes that reserve the institution of civil marriage to one-man – one-woman relationships.”

Lambda Legal, which is representing the case's 8 plaintiff couples, appealed the ruling to the Ninth U.S. Circuit Court of Appeals in San Francisco, arguing that Nevada's ban violates the constitutional rights of gay couples.

In its brief, filed Tuesday, the state argued otherwise.

“Nevada law that defines marriage to be between a man and a woman is legitimate, whether measured under equal protection or due process standards,” the brief states. “The interest of the state in defining marriage in this manner is motivated by the state's desire to protect and perpetuate traditional marriage.”

“Nevada's statutes evince a strong encouragement of marriage in its traditional form. These laws are not based on policy whimsy; they are grounded in policy as deeply rooted as any that exists in Nevada law. … They define Nevada society.”

Lead plaintiffs in the case are two women in their 70s who have raised 3 children and have 4 grandchildren. Beverly Sevcik and Mary Baranovich have been together more than four decades.

In 2002, Nevada voters overwhelmingly approved a constitutional amendment defining marriage as a heterosexual union. Nevada in 2009 began recognizing gay and lesbian couples with domestic partnerships, which offer far fewer benefits than marriage and are not recognized by the federal government.

Last year, lawmakers gave initial approval to repealing the ban and legalizing gay nuptials in Nevada. A second vote is needed before going to voters in 2016.