In our travels, we've found usage in CG's about the same in states where it's legal as in states where it's not. When it was legalized, the place we noticed the usage increase here in Colorado was skiing. Seems a lot of out-of-state people want to experience the Rocky Mountain High!
I'm not sure what the OP's concerns were but we've found alcohol to be at the root of unruly campers far more than those getting high.
What's interesting is that I've discovered a significant number of Coloradoans in their 50's, 60's, and 70's partake, mostly at home. Haven't heard if they get an AARP discount! ;)