Their trackage was likely the most extensive narrow gauge in the East Bay, if not the entire Bay (except the NPC). The last of the narrow gauge track was removed in 2000 when the development of the remaining Hercules Powder Co. land was underway. The bridge that crossed the SP main at Hercules Point had double track narrow gauge that extended to onto the wharf. I can't imagine anywhere else a double track narrow gauge line crossed over a double track standard gauge line.

The narrow gauge line extended all the way out to present day Refugio Park/valley in Hercules and passed under I80 and the Santa Fe on its way out towards Franklin Canyon.

The power used was variety of fireless steam engines and battery powered electrics and in later years, gas powered porters (natural gas I believe). A decent amount of narrow gauge infrastructure and equipment made its way to Disneyland in Anaheim and is still in use today.

Images of America by Arcadia Publishing just released the Hercules book on June 7th and it has a good coverage of the narrow gauge. Could have covered more, but its the best coverage I've seen yet. I'm still kicking myself for not photographing the last of the narrow gauge line and taking some of the rail as they were removing it in 2000. I was too young and busy shooting SP tunnel motors in Hercules to think of the narrow gauge!