The Democratic and Republican parties in Colorado hold their caucuses today at 7 p.m.
The caucuses start the process of determining who party nominees will be in races with more than one candidate (for Democrats, most notably the race between Bennet and Romanoff, but also many state legislative posts). The precinct committee people selected there are also the people who choose the people who run the non-legislative part of the major political parties.
Delegates from precinct caucuses participate in county level meetings and meetings with particular legislative office districts that nominate party candidates for offices at those levels, and participants in meetings at the county level in turn send delegates to state level meetings that nominate people for state level offices. Party platform issues are also dealt with, often as an afterthought, at each level of the process.
We have a government by people who show up for people who show up. With the exception of the 2008 caucuses that influenced who the Presidential nominee of the major political parties would be, attendance is usually about 1% of the registered voters with a party affliation who are the only ones allowed to vote at a caucus.
A caucus vote is equivalent to 100 votes in a political primary. It takes a couple hours, but in exchange you have much more of a say in how your state is run.