West of Lyons in the North Foothills Open Space, the Hall Ranch has a 12 mile trail network open to hiking. The main route is the 3.7 mile Bitterbrush Trail which leads up to the 2.2 mile Nelson Loop. Combined, the total mileage is 9.6 miles. However, there are several other side trails worth exploring, especially on busy weekends.The trails are mainly packed dirt and are very exposed with little shade. To reach the Hall Ranch trailhead from Boulder, head north on SR36 for abou 14 miles. Turn left heading northwest on SR36/66 for 1.4 miles into Lyons. Turn left heading south on SR7 (South St. Vrain Drive) for 1.4 miles and look for the trailhead on the right.
From the trailhead, follow the Bitterbrush Trail climbing up 3.7 miles to the Nelson Loop. The 2.2 mile loop is best ridden clockwise. Then return downhill via the Bitterbrush Trail back to the parking lot. The total mileage is 9.6 miles. There is one additional trail open to mountain biking, the Antelope Trail. It is a one mile trail from the middle of the Bitterbrush Trail that leads to an alternate parking area off Antelope Drive just north of Lyons.
Note: This trail system is very crowded on the weekends, especially from 10am to 4pm. It is very popular with mountain bikers. Consider exploring this trail system early on weekdays.