With summer temps range from 70s to 80s, low humidity and usually sunny days, any outdoor activity you choose is pretty much guaranteed weather cooperative. Hiking is one of the most popular activities and there are a number of trails, from easy to experts only, please, for your enjoyment. If tires are your mode of transportation, mountain biking could be for you.
Trails vary from beginner to speeders - all legal of course.
Maybe a rafting or kayaking trip on the Colorado River might wet your interest. The European-style alpine village of Vail is just 110 miles from Denver and about 140 miles from Grand Junction. I-70 West from the Denver area. The Town of Vail operates the largest free public transportation system in the country from the east side to the west side, making the Village pedestrian-friendly. The entire family can enjoy a number of activities together.