"I am aware of where the private land is where I hunt though. The land owners aren't required to make their land in Colorado. So, it's up to the hunters to know where the private land is."
Same here (Illinois now, formerly Wisconsin). Although in Illinois, it's pretty easy to keep track of because there's so little public land available to hunt on, you learn it pretty quick if you hunt at all.
It's funny, I grew up in northern Wisconsin, started hunting in the 1970s. It seemed nobody really cared about trespassing. Of course, that was before hunting became the big business it is today. Nowadays, seems everything is posted.