Return to Interstate 8 and proceed east approximately 4 miles to the Morena exit. Turn right (south) and continue south on Morena Road across Old Highway 8 approximately 2.3 miles to the paved Morena-Stokes Valley Road. Turn right (cast) and follow road past Honor Camp to the Four Corners ORV area (3 miles). Turn right at Four Corners and follow dirt road toward the Los Piños summit and fire tower.

Stop 5a (Figure 16) is approximately one mile from Four Corners at a pull-off area on the east side of the road. It will give us an opportunity to traverse through a section exposing the wide variety of rocks types found within this pluton. The oldest rock type is a hornblende gabbro (Outer Group) that was interpreted (Walawender, 1976) to be the result of extreme fractional crystallization of olivine, calcic plagioclase, and lesser amounts of pyroxene from a water-rich, high-alumina basaltic parent. The resulting gabbroic daughter melts became water-oversaturated and produced textural variants that include pegmatites, aplites, and comb structures. These high-level fractionates were then intruded by more parental melt to form the belt-like zone of cumulates (Inner Group) that cut across the pluton. Hornblende-bearing peridotite and anorthosite in elongate, dike-like masses and conflicting relative ages within this belt suggest multiple periods of injection and subsequent cumulate remobilization.