On the trip to Big Picacho, the greatest difficulty encountered was finding the roadhead. The information obtained was sketchy and difficult to follow. Thanks to Mario Gonzalez, who was able to ask directions from several natives, the trip was successful.
In hopes of helping someone else, I measured the distances between various turning points on the way out.
Road log starting from the intersection of highway 5 and 3 in Mexico.
1. Turn West on hwy. 3 and go 20.4 mi to a dirt road. The road is identified by two signs:
1. sign with blue letters - SARH plus more writing
2. sign with red letters - Villa DelSol
2. Turn left on the dirt road and travel 4.2 mi to another Intersection, identified by a sign with green lettering: Programa Valle Chico, Col SPM
3. Turn left at this intersection. This is the road that crosses the dry lake. Asa check point, after .4 mi there is what looks like an abandoned rancho. (corral & house). The first part of the road crosses a sand dune like area before entering the dry lake. On the dry lake, you will pass several whitewashed tires standing parallel to the road. 10.6 mi. after the "abandoned" rancho, you come to another intersection identified by a whitewashed tire standing perpendicular to the road you are traveling on.
4. Turn right at this intersection. After about 1 mi. there is some soft sand where some cars may have trouble crossing. At 1.2 mi, after making the above turn, there is a rancho on the right, and a "Y" Intersection.
5. Take the road to the right, which goes right along the fence of the rancho, for 1 mi.
6. At this point another dirt road comes in from the left. Continue on the same road you are on for another 5 mi. until you reach the roadhead. This last 5 miles seem to parallel the mountains, but it does get there eventually.