PHOENIX — Arizona Republicans are heading to the polls to help pick a presidential nominee.

Polls, which opened at 6 a.m., will close at7 p.m. MST, although many Republicans voted before the day even started.

In the state's two most populous counties, a majority of Republicans who received early ballots had returned them by late last week, officials said. In Pima County, a third of the registered voters overall had already cast early ballots.

Just under 52 percent of the state's registered Republicans voted in the state's 2008 presidential primary, but Maricopa County Election Director Karen Osborne said turnout this year likely will be in the 40-50 percent range.

There's lower interest overall than four years ago due to the lack of a Democratic contest, she said.

Home-state candidate U.S. Sen. John McCain won the Arizona primary four years ago en route to winning the Republican nomination.

This year's Arizona's primary was overshadowed by the Michigan contest on the same day.

Both states have nearly the same number of delegates, but Arizona's contest is winner-take-all, giving a candidate not expecting to win the statewide vote little incentive to campaign in Arizona.

Former Massachusetts Gov. Mitt Romney was the only candidate to run ads in the state. There was little in-person campaigning by candidates other than right before a debate held in Mesa last week between Romney, former Pennsylvania Sen. Rick Santorum, former House Speaker Newt Gingrich and Texas Congressman Ron Paul.

The debate itself focused on national issues rather than Arizona topics, though illegal immigration and border security did get some attention.

Marilyn Riggs, an elementary school employee who described herself as a liberal to moderate Republican, cast her vote for Paul at a school on the edge of downtown Phoenix. She said Paul is the best candidate to shrink the size of the federal government.

"It was not a difficult decision," said Riggs, who picked Paul as her candidate a few months ago. "I am tired of some of the rhetoric from the other candidates. I am tired of some of the ultraconservative issues that have nothing to do, in my opinion, with what the government should be doing and how to govern and how to spend the money."

Husband and wife Joe and Evelyn Turany, of Phoenix, both voted for Santorum, saying he offered the most conservative values and comes off as the most honest.

"He's a lesser of four evils," said Evelyn Turany, a 75-year-old retired high school teacher. "He's more conservative, and I'm a little tired of the government providing funds to kill babies."

Both said that Romney was too rich and too arrogant to win their favor. "It would be like exchanging one snob for another snob," Evelyn Turany said. "There is no way a man that wealthy can understand my position."

In Flagstaff, Tim Pomeroy, a 48-year-old locksmith, voted for Santorum, saying he was drawn to the senator's message. "I just like everything he's saying," Pomeroy said. "It's going to be lower taxes and smaller government. The larger the government, the smaller the citizen."

Jerry Slade, 63, of Flagstaff, voted for Gingrich. He said Gingrich was able to work with Democrats in the past and has a solid backbone in politics. "If he was our nominee, I think he would be one of the strongest ones to straighten out our country," Slade said.

Arizona will send 29 delegates to the Republican convention. That's half of the normal allotment and reflects a penalty imposed because the primary is being held before March 6.