Supporters of Proposition 8, which bans same-sex marriage, claimed victory, but their thin lead could still be threatened by absentee ballots yet to be counted.
Gay rights advocates always knew they were in for a tough election night.
"Buckle your seats, honey, it's gonna be a bumpy ride," said Kate Kendell of the National Center for Lesbian Rights.
Together, both sides raised more than $70 million making Prop 8 more expensive than any contest other than the presidential race, Blackstone reports.
Some news organizations have projected that the proposition will pass, but CBS News has yet to make a projection due to the uncounted absentee ballots.
With 97 percent of precincts reporting, 52 percent have voted yes on the measure and 48 percent have voted no. (Latest results are available on the California state results page)
Similar measures have prevailed previously in 27 states, but none were in California's situation - with thousands of gay couples already married in the aftermath of a state Supreme Court ruling in May.
The office of San Francisco City Attorney Dennis Herrera said he will file a legal challenge against the validity of the ballot measure to change the constitution if it passes.
Similar ballot measures banning same-sex marriage were up for vote in Arizona and Florida. CBS News projects that Arizona voters have passed the same-sex marriage ban.
Elsewhere, CBS News projects that voters in South Dakota voted down Measure 11, which would have prohibited abortions except in cases where the mother's life or health is at a substantial and irreversible risk, and in cases of reported rape and incest. If it had passed, it would likely have triggered a legal challenge which could have lead to the U.S. Supreme Court and a reconsideration of the 1973 Roe v. Wade ruling that established the right to abortion.
In Arizona, voters rejected Proposition 202 which would have modified laws relating to the employment of unauthorized aliens; the law would also have fined employers who pay improperly reported cash wages.
In Arkansas, a single parent or a couple who are not married will not be able to adopt a child or serve as a foster parent; voters approved an initiative which would mandate that only married couples can do so.
In Colorado, CBS News projects that voters rejected Amendment 48, which would have defined the term "person" to include any human being from the moment of fertilization.
Colorado voters are also deciding on Amendment 46, which would prohibit discrimination by the state or granting preferential treatment to any individual or group on the basis of race, sex, color, ethnicity, or national origin in the operation of public employment, public education, or public contracting. According to a poll taken in late October by CBS station KCNC in Denver and the Rocky Mountain News, 53 percent of registered voters in Colorado support the amendment.
In Maryland, voters approved video slot machines.
In Massachusetts, voters had to decide on a ballot measure eliminating the state's income tax. Question One proposed eliminating the 5.3 percent income tax by January 2010. According to projections, the ballot question was not passed.
In Michigan, voters passed (by a margin of 63% to 37%) a legislative initiative to permit the use and cultivation of marijuana for specified medical conditions. Also approved: An expansion of the use of stem cells from human embryos for any research permitted under federal law.
In Nebraska, CBS News projects that Nebraska voters are going to pass Measure 424, a constitutional amendment banning affirmative action, by prohibiting the state from discriminating against, or granting preferential treatment to any individual or group on the basis of race, sex, color, ethnicity, or national origin in public employment, public education or public contracting, although there would exceptions for certain federal programs.
And in Washington State, voters approved, 59%-41%, Measure 1000 which would permit terminally ill, competent, adult Washington residents, who are medically predicted to have six months or less to live, to request and self-administer lethal medication prescribed by a physician.
Here is a state-by-state roundup of results for the most noteworthy ballot issues:
In addition, CBS affiliate KPHO reports that voters rejected Proposition 200, the Payday Loan Reform Act. Proposition 101, which would amend the state constitution to provide that no law shall restrict a person's freedom to choose a private health care plan or system of their choice, is not yet decided.
In addition, CBS Station KPIX reports that voters have approved a proposition on humane confinement of farm animals (Proposition 2); rejected requiring utilities to generate 20 percent of their power from renewable energy by 2010 (Proposition 7); and approved bond measures for funding children's hospitals and helping veterans purchase homes and farms. Results on Proposition 11, which would change the way legislative district lines are drawn, are too close to call.
In San Francisco, KPIX reports that voters turned down a measure that would have barred police from arresting prostitutes. The city couldn't technically legalize prostitution since it's against state law, but the proposal would have barred local authorities from investigating, arresting or prosecuting anyone for selling sex. Also, an attempt to rename a local sewage treatment plant after President Bush went down the drain.
Also on the ballot: CBS Station KCNC reports that voters rejected Amendment 47 would ban mandatory union membership and dues by employers; and also rejected Amendment 51, which would raise state sales taxes to fund long-term care for persons with developmental disabilities.
Also, dog racing has gone to the dogs: CBS Station WBZ reports that voters approved a ban, 8 years after rejecting a similar measure.
The AP reports that voters rejected an elimination of term limits for legislators.
Click here for updated, complete election results by state.