The mayor of Denver Michael Hancock made efforts to mark the first year of same-sex civil unions in Colorado with a special reception.
Since coming into effect a year ago today, 1 March 2013, Denver has issued 859 civil union licences.
Although same-sex marriage is not currently available in Colorado, civil unions allow some equal rights including inheritance and parental benefits.
The unions may also allow same-sex couples to make medical decisions on behalf of ill partners.
At the reception, Hancock said the state “has made great strides toward bringing down the walls that divide.”
Colorado voters passed a constitutional ban on same-sex marriage in 2006.
In a historic day for the US state of Colorado, Governor John Hickenlooper signed civil unions into law on 22 March 2013, following several attempts to pass the legislation in recent years. The law took effect a year ago.