Ride up FR 578, heading north. At the 1 mile mark, keep right at the fork (the left road is FR 550, you will reach this junction again via 550 a few hours later). After a short downhill, you climb moderately on rutted road. There are some wet spots from the runoff into Hermosa Creek. After 4.5 miles, you encounter a series of switchbacks and the climb becomes increasingly steeper for over 2 miles! After passing an old mine/parking area, the climb eases up for the 0.5 miles until the CO Trail junction.(This is Bolam Pass) Keep left(south of a tiny lake) and start the singletrack!
The CO trail is not too technical, just lots of exposed rocks. You just feel the fatigue more because of being over 11,000 ft and the energy expended from the road climb! Just follow the cairns that mark the trail after going above treeline. Turn left at an intersection with a rutted out doubletrack.(8.8 mi mark) After about 1.5 miles of ups and downs, ending with a steep, loose climb, turn right at the marked continuation of the CO Trail.
After another moderate 1 mile climb, head downhill for 1.5 miles. Begin the final 2.6 mile ascent to Blackhawk Mountain! The climb progresses from slight grade-->steeper/rocky with some tight switchbacks-->final very steep climb! After completing all this, you have reached Blackhawk Pass, elevation 12,000 feet!! After taking in the view that rewards your hard work, start the downhill!
The trail descends in a southeast direction from the summit. In other words: standing at the wooden post marking the summit, turn your back to the steep trail you just ascended; you can see the downhill trail dropping to a creek. The descent to the creek is the most technical downhill section(loose, steep with a couple of tight switchbacks). Then it's a fast descent the rest of the way! There are a couple of short climbs, but no big deal with the momentum you generate. Reach the intersection with FR 550(18.7 mi mark), make a left. The valley you see on your right as you descend 550 is Hotel Draw. After about 4 miles, reach the junction with FR 578, go right and reach your car after 1 mile!