If you're going to be in downtown CS, there are quite a few bike racks throughout. If on the outlying areas, they are hit and miss. There are many bike paths and bike lanes throughout the city and it's a great place to be a cyclist. I'm sure there are thieves all around the city, but a lock, any lock, might discourage someone from walking off with your bikes during the day and early evening. At night, all bets are off. Estes Park I know nothing about. I grew up in the Springs and my mom and sister still live there but the last time I was in EP, I may have had a on diaper (I'm 53 now). I know a lot of tourists head there and it's a smallish town, but I would still recommend a lock for expended absences from your bikes.