State law defines marriage as between a man and a woman, but city officials say equality provisions in the state's Constitution should take precedence.
It also defined marriage as between a man and a woman.
Marriage in Northern Ireland is legally defined as between a man and a woman.
Voters were asked whether they approved of a popular initiative to amend the constitution defining marriage as between a man and a woman.
Oregon is one of 13 states without laws defining marriage as between a man and a woman.
The measure was Proposition 8, defining marriage as between a man and a woman.
The amendment easily passed, although state statute already defined marriage as only between a man and a woman.
"Through my Christianity, I define marriage as between a man and a woman," she said.
Forty-one US states currently define marriage as between a man and a woman.
Legislators will consider a proposed amendment to define marriage as solely between a man and a woman.