Colorado has gone to all-mail-in ballots. Those ballots were mailed out several weeks ago. The counties also have a system of drop boxes at libraries and other public locations, where you can leave your ballots. They collect them every day until the 5th of November.
There is an online application you can access that will tell you if the County Clerk has received your (so far unopened) ballot. Political campaign organizations subscribe to that data (at a hefty fee) to target their calls and letters. Once you have turned in a ballot, the calls and letters stop.
I just drove by my voting area, and they still have walk-in voting.