If you are registered with a party, Tuesday is the last day to change or withdraw your affiliation to vote in a different party's primary.
If you are unaffiliated, Tuesday is the last day to either affiliate or, without affiliating, state a preference to get one of the major party's primary ballot in the mail. If you are unaffiliated and don't make such a choice, you will get both major party ballots in the mail.
You can do this at www.GoVoteColorado.com or come into the Courthouse.
If you are not registered at all, you can wait until Election Day, June 26, to register, but then will need to go to one of the voting locations in Telluride or Norwood.