Hall Ranch is in Lyons (past Boulder). Rated: Intermediate with a couple of ADVANCED rocky technical sections. It is typical to start at the Lower Bitterbrush trailhead, do the loop and then come back down this awesome, technical downhill.
Directions: From Boulder, take US 36 / Foothills Hwy. north toward Lyons. Turn left on Hwy 66, then left on Hwy 7 / St. Vrain Rd. in Lyons. Trailhead is on the right. http://g.co/maps/w5fk8