It's getting tougher these days to find a trail in Colorado that allows dogs off-leash, but they do still exist. The Mayflower Gulch Trail near Frisco offers six miles of out-and-back along with two spurs, so there's plenty of room for your pooch to run free (dogs must respond to voice commands). With its 1,478 feet of elevation gain from 10,955 feet, the trek is moderately difficult, but pockets of dense forest and mining ruins offer breathers for exploring. Pups love to dip into Mayflower Creek, which runs along parts of the trek, and in winter, this year-rounder is fun on cross-country skis or snowshoes.
fs.usda.gov