On Sunday night, with 85 percent of precincts reporting, Romney had 49 percent of the votes, and Gingrich had 22 percent.
Just about 830 votes separated Gingrich and Paul.
Paul had 19 percent.
Santorum was in fourth, with 10 percent.
Not all the votes have been tallied in Nevada's largest county.
The Las Vegas Sun reports that Republican Party workers confirmed ballots in multiple precincts exceed the number of people who signed in to vote.
The GOP candidates have been hitting Colorado hard before Tuesday's caucus, and Monday will be filled with campaign stops as candidates make one last push.
Frontrunner Mitt Romney was in Colorado Springs on Saturday, and on Monday he will hold an event in Grand Junction and at Arapahoe High School in Centennial.
Newt Gingrich will rally Monday morning in Golden, and a few hours later attend the Colorado Energy Summit at the School of Mines.
Rick Santorum will also attend that same energy summit, and on Monday night will hold a rally at the Cable Center in Denver.
Ron Paul was in Colorado last week a few times, but won't be returning before Tuesday's caucus.
With four candidates still alive, Colorado's GOP caucus has become even more important.
9NEWS political analysts have said our state could weed out a bottom contender, and perhaps set the pace for the rest of the western United States.
Even though Mitt Romney won Colorado in 2008 with 60 percent of the vote, this time 9NEWS Political analyst Floyd Ciruli says it's not in the bag for Romney.
"He's going to have some concern about the fact that he is now seen as the more moderate person - four years ago was the conservative against John McCain so he's seen as the more moderate person against this array of conservatives," Ciruli said.
A caucus is like a town hall meeting.
In this case, a group of Republicans will decide who the rest of the population gets to vote on.
Somewhere between 50,000 to 60,000 Republicans are expected to participate in this caucus according to GOP State Party Chair Ryan Call.
The caucus starts with some introductions, then there's an election for a precinct leader, and following that, people can speak on behalf of their candidates.
The caucuses start at 7 p.m. on Tuesday, and are expected to last about an hour and a half.
Participants are expected to arrive at 6:30 p.m.
You must be a registered Colorado voter and affiliated with the Republican Party as of December 7.
You must also have lived in your precinct area for at least 30 days.
After caucus-goers circle their candidate on a presidential preference poll ballot, they are collected and handed over to the county party, then given to the state party.
The results show support for the winner, but won't bind any of Colorado's 36 Republican delegates to support a particular candidate at the national convention.
The Minnesota Republican caucus is the same day as Colorado's, and Maine Republicans started their week-long caucus process on Saturday.
The results from that state will be available next Saturday.
For more information on where to find your precinct caucus, click here: http://www.9news.com/news/politics/247232/139/Colo-Republican-caucus-Tuesday
For details on where the candidates will be in Colorado, and times, click on a candidate's link below:
Mitt Romney: http://www.mittromney.com/states/colorado
Newt Gingrich: http://www.newt.org/events
Rick Santorum: http://www.ricksantorum.com/events
Ron Paul will not be in Colorado again before Tuesday's caucus
9NEWS.com will be live-streaming Newt Gingrich's 11:30 a.m. rally from Golden, Rick Santorum's rally between 3 p.m. and 5 p.m. from Golden, as well as Mitt Romney's 6:30 p.m. rally in Centennial.
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