With pot already legal for use by adults in four states and the District of Columbia, a win for legalized marijuana in California alone would make the entire West Coast a cannabis-friendly zone, completing a geographical march begun in Washington state and Oregon.

Potential victories in Arizona, Nevada, Massachusetts and Maine would fill in much of the rest of the West and extend recreational use to the Northeast. Opinion polls show voters favoring the initiative in all five states.

In addition, measures to legalize medical marijuana or expand its use are on the ballot in North Dakota, Montana, Arkansas and Florida.

Twenty-five states already have legalized cannabis in some form, whether medical or recreational, or both.

In California, where medical marijuana has been legal since 1996, a recent poll by the Public Policy Institute of California showed 55 percent of likely voters supported a ballot initiative that would authorize the state to tax and regulate retail cannabis sales much like it does alcoholic beverages.

That was similar to the numbers favoring legalization from opinion polls in Massachusetts and Maine. Slimmer majorities or pluralities also point to legalization in Arizona and Nevada.

Approval by California alone, America’s most populous state with 39 million people, would put nearly a fifth of all Americans living in states where recreational marijuana is legal, according to U.S. Census figures. That number grows to more than 23 percent if all five state measures pass.

Backers of legalized marijuana sales have tried for decades to win support at the ballot box, with little success until the past few years, starting with victories in Colorado and Washington state in 2012.

Experts say the latest initiatives include more sophisticated regulatory mechanisms aimed at keeping cannabis away from children and banning the involvement of criminal gangs and drug cartels. Public opinion has rapidly swung toward favoring legalization.

“It’s changed in the minds of these voters from being like cocaine to being like beer,” said University of Southern California political scientist John Matsusaka.

Legalization by even a few of the states where measures are on the ballot could prod the federal government, which still classifies marijuana in the same category as heroin, to begin rethinking its laws and policies, Matsusaka said.