This is former South Pacific Coast (SPC) #6. The Southern Pacific shipped it south to the SP owned narrow gauge between San Bernardino and Redlands. There it was relettered as SP #6. Thus when the paint faded it appeared to be SSP.
The photo is identified as having been taken in Los Angeles in 1915.
Journal of the Southern Pacific Narrow Gauge Historical Society used this photo in one of two issues about the narrow gauge. The line was built by local interests as a side-of-the-road steam dummy line and was later acquired by the Southern Pacific.
Brian Norden