The Jawbone/Lone Pine branch was limited to smaller power. I don't think anything bigger than an Mk in steam era was used. Once Trona started dragging trains into Searles, I think bigger power was used Mojave-Searles. It seems I have seen a picture of a smaller cab forward, but I don't know if all the AC classes were ever permitted.

In the diesel era, it seems an Alco RDS5 worked to local to Owenyo before the narrow gauge gave up. After that, a single SD7/9, GP9 or SD39 was typical. The SD39 seems an odd choice (other than they must have been at Mojave for helper service and maybe other locals (Creel and Mountain?). The North/East end of the line was 75# rail when it was scrapped. Searles to Mojave is a different story with heavier rail and enough traffic that it could almost be considered a secondary main more than a simple branch. I think six axles were the norm here except for when the tunnel shoo fly was limited to B-B units.

Some F-units made it up towards Lone Pine, but not sure if this was limited to movie trains. Searles-Mojave must have got F-units and SD9s before the SD45s arrived en masse.

Does anyone know some better info? I also wonder how much traffic (extra trains?) actually went to China Lake NOS outside Inyokern.