Not that long really. Colorado only went from a primary to caucus system in 2004 and this is the first year without a presidential poll of any kind which is a process practically unheard of in any state in in any past election cycle. Which explains the attention it is getting.
In the 1990's a presidential primary was organized that was abandoned beginning in the 2004 election to save money. The caucuses and state convention were still held, they just didn't decide the candidate(s) the national delegates would be pledged to vote for in the three intervening presidential elections.
The Republicans used a straw poll in the last election that bound the national delegates, but abandoned it because our precinct caucuses are so early we were pledging delegates to candidates no longer in the race at the convention.
That said, both parties now want to bring back the presidential primary as on both sides it has pretty much been a CF, to use an old Army phrase.