What are some of the best hiking / biking trails in Boulder?

My new favorite is Eagle Trail just past the Boulder Reservoir from Jay and 51st. They allow mountain biking and theres even some fun single track along the way. Its a moderate loop with a couple of fun hills and offers great views of the Flatirons and the mountains around. It is dog friendly and there is a pond where dogs can swim. You can even ride horses on it although Im not a fan of the horse "piles" along the trail.

Boulder has several biking trails.

The Boulder Reservoir Loop is a nice after work ride. You can catch the trail along Wonderland lake which will take you past Dakota Ridge. Continue under the free way and turn left. You will then go through a cattle gate and continue along the mesa and out and around the Boulder Reservoir.

If you have a little more time and leg power another nice ride is to pick up the Boulder Canyon trail at Eben G. Fine Park and continue up Boulder canyon at the top you have to transition back on to the road for about a mile until you see the tunnel. Right before the tunnel look to your right and you will see the single track that you can ride up to Betasso Preserve Loop. The climb out of Boulder Canyon is steep for about 300 yards and then becomes a nice switch back ride. From my house in North Boulder it is about a 21 mile ride round trip. The Betasso Preserve is closed to biking at times so be sure to check the Boulder Parks and Rec Website before you go.

I have also heard Dowdy Draw is a nice ride out off of Marshall Mesa, but I have not ridden it.

A couple other rides to check out close to Boulder are Walker Ranch, Halls Ranch (I prefer the Apple Valley Side) Heil Ranch, and Miller Rock.

Cyndy and I have also found Anemone Hill Trail a good option if you want a quick hike that is not crowded. Most people tend to go up Sanitas, but if you go South instead of North from the parking lot you work your way up to the Anemone Hill Trail head. It is a pretty hike with nice views down to Boulder Creek. When you get midway up you will see what we call the Candy Cane you can turn right and continue up here or go straight ahead and drop and hike above Boulder Canyon, both are good options.

There is also some great hikes on the other side of the Boulder Creek. Settler's Park is a great short hike, with some very cool rock formations to climb around; it is where the first white settler's spent their first night in Boulder, hence the name. A little further to the north is Mount Sanitas, which is a long loop trail, the back half being steep and rugged, and the front half being wide and mellow. But ultimately, Chautauqua Park at the base of the Flatirons offers the most variety of short and long trails, and you can't beat the view. For biking, Flatirons Vista Trail, a little ways south on Highway 93 is great. For something a little more intense, take the Flagstaff road about five miles up until you get to the Walker Ranch. Just to name a few great places to get into the mountains.