Open all year because there is NO WATER--ie., no water lines to freeze. But check out the elevation because the San Luis Valley is one of the coldest places in Colorado in winter. If you don't mind single digit or negative nighttime temps in your RV, then feel free to stay. But it is not "free" unless you have a Colorado fishing or hunting license (which costs $9.75 annually for a Colorado resident senior like me). Check the CPW website for more info and possible closures.