SAN FRANCISCO – Voter support for legal marijuana in Washington and Colorado is spurring similar campaigns in California and three other states that together may bring pot within lawful reach of nearly one in five Americans.Advocates are seeking the signatures of registered voters in California, Arizona, Oregon and Alaska, with a combined population of 49 million, to put the question on ballots in 2014. Colorado and Washington last year legalized marijuana for 12.1 million people.“Because of Colorado and Washington, it’s created a cannabis tidal wave across the country,” Mike Jolson, 45, a legalization activist in Santa Cruz, said by telephone. “We want to capitalize on this wave.”Washington and Colorado became the first U.S. states to legalize recreational marijuana through referendums last November, defying federal law that has prohibited pot since the 1930s. In August, the U.S. Justice Department said it wouldn’t challenge the states, opening the door for others.In Washington state, regulators are finalizing rules for growing, processing and selling marijuana ahead of a Dec. 1 deadline to begin issuing licenses. In Colorado, which has finished setting its rules, voters will decide next month whether to tax retail sales at rates of as much as 25 percent.