DENVER -- Colorado Republicans and Democrats are getting ready for the caucuses Tuesday.
It's arguably the second most important political event of an election year, behind the general election.
While some states hold primaries similar to a general election with ballots cast privately, Colorado has a caucus run by each party. The caucuses bring thousands of people into precinct locations across the state.
Volunteers from Bernie Sanders' campaign office on Colfax Avenue were busy making last-minute calls Monday.
"We have different teams," said Dulce Saenz, Colorado director for the Sanders campaign. "Some folks are doing phone banks all day, others are out walking and knocking on last-minute doors."
It was the same kind of action at Hillary Clinton's Denver campaign headquarters.
"Some people we ask don't know about the caucus process, so they don't know that they have to go in person," said Kellie Lange, a volunteer with Clinton's campaign.
They're ready to caucus. But do you know what to do?
"It's a meeting of friends and neighbors at a location usually right in their neighborhood," Colorado Democrats Chairman Rick Palacio said.
Democrats and Republicans, who registered with their party before Jan. 4 can go online to their party’s website to find their precinct location. The caucuses start at 7 p.m.
RELATED: Democrat caucus locations
RELATED: Republican caucus locations
And one of the most important things participants will do is vote on which of their neighbors will become delegates. Those delegates will then cast their vote for leaders at every level -- from U.S. Senate to president -- at the county convention.
The big difference between parties this year is that Democrats will have a presidential preference poll.
"We'll have a count of people that actually showed up," Palacio said. "And who showed up for Hillary, who showed up for Bernie."
Republicans will not have the presidential preference poll.
"Once you take a poll and you make it worth an actual delegate, so you're going to bind delegates, it's now an election," Colorado Republicans Chairman Steve House said. "The parties are not equipped to run an election. We're equipped to run a poll so we've got great concerns about loopholes, potential fraud."
But with five candidates still in the running, the Republican race is still expected to dominate the caucus conversation.
"This is probably the most interesting presidential election of my lifetime, let alone most people that go to caucus," House said. "They will actually ask people that are running for delegates, 'Who do you support?' And some of their votes may be based on what those answers are."
Caucuses are expected to last about two hours. While they start at 7 p.m. at each precinct location, participants are asked to arrive early.