PHOENIX (AP) -- Arizona Republicans will head to the polls Tuesday to help pick a presidential nominee.
Polls are open from 6 a.m. to 7 p.m. MST, although many Republicans have already voted.
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 says turnout this year likely will be in the 40-50 percent range.
Osborne says there's lower interest overall than four years ago due to the lack of a Democratic contest. Michigan is holding its Republican presidential primary Tuesday.
Mitt Romney is regarded as the front-runner in Arizona, partly because of his tough stand on illegal immigration. He picked up the endorsement of Gov. Jan Brewer on Sunday, and did well in the state's GOP presidential primary in 2008.
A closer race between Romney and Rick Santorum is expected in Michigan. Neither of the other two contenders, Newt Gingrich or Ron Paul, has made much of an effort in either state.
At stake Tuesday are 29 delegates in Arizona and 30 in Michigan.
Tuesday's voting comes ahead of an intense week of campaigning across the country.
March 6 is Super Tuesday, when 10 states will hold GOP nominating contests as far apart as Virginia and Alaska. Wyoming also holds county conventions beginning that day.