You are in the CarrTracks website Picture Gallery.
An empty ballast train (Extra 3326 East) races through Muldoon on August 21, 1978.
Train symbol APLAA (Auto Parts West) races by one of the few remaining semaphore signals just north of Muldoon at milepost 43 on December 14, 1977.
The lower signal on the mast is for the hotbox detector. There was a Type A hot box detector at milepost 45.8. The Type A was one of the first detectors on the SP and required a crew member to look inside a signal box to get the axle count. When the detector went off it would light the letter H on a signal like this ahead of the train. Other trains could not go over the detector until the crew member on the train with the hotbox reset the display. The signal in the picture is equipped with a light that displayed the letter W (for wait) when the detector went off. Disk 100