Overview:
This is a classic ride west of Boulder, CO. It is mostly intermediate with some advanced sections. Follow Flagstaff Road for about 7.5 miles from Boulder and you will come to the Walker Ranch Loop Trailhead. But since I am based in Denver, I will describe the directions from the Crescent Meadows Trailhead off of Gross Dam Road.
To get to the trailhead from Denver, you have to drive a lot further. Drive I-70 west for about 12 miles. Take Highway 58 West for about 5 miles until you get to the intersection with 6th Ave and Highway 93. Turn right onto Highway 93, going north for about 12 miles until you get to the intersection with Highway 72 (Coal Creek Canyon Road). Turn left onto Coal Creek Canyon Road. going west for about 7.4 miles until you get to the intersection with Crescent Park Drive on your right. Turn right onto Crescent Park Drive and go about 1 mile until the road T's into Gross Dam Road. Turn right onto Gross Dam Road and descend for about 2 miles. The trailhead will be obvious on your right, shortly after crossing some railroad tracks.
You are about 2.1 miles from the start. Time for the hike-a-bike section. Dismount at this sign and start hiking. Be careful for the stairs are very steep.
You are about 3.3 miles from the start. Turn left at this intersection and continue on the Walker Ranch Loop trail. Going straight will bring you to the Ethel Harrold Trailhead in 1/4 mile.
You are about 4.9 miles from the start. This is the trailhead most people start at if you are coming from Boulder. If you want more mileage, you could start at the Meyer's Homestead trailhead and do the Walker Link trail, about 3/4 mile one way.
For the adventurous who want more miles to ride, start from here and do the Walker Ranch Link. For the even more adventurous, add on the Meyer's Homestead trail, a 2.6 mile jeep road one way.