It would be an uphill battle to be sure, but in every state that had a referendum (including the far left mecca of California), homosexual marriage lost. Clearly, voters are not in favor of homosexual marriage, regardless what the media claims.
A constitutional amendment would not pass in California because the Democrats are firmly in control of the legislature. But the Republicans now control most of the state legislatures and could pick up some more.
Check Maryland.
That was true until 2012, but in 2012, Maine, Maryland and Washington voters passed initiatives in favor of same-sex marriage, and Minnesota voters rejected an initiative to prohibit same-sex marriage.