That tender commonly known on the SP as a "whaleback" tender was very common on the SP particlarly for the many consolidations the SP ran. Consolidation Tenders were swapped often and from year to year the same locomotive might have a Vanderbilt, whaleback or rectangular tender. It was an efficient solution as the SP did not use coal on most lines after 1905. The tender could be the easiest shape. I believe whalebacks were mostly built at the Sacramento shops. After all California, Texas and Louisiana had a great deal of readily available oil but little usable coal. In addition, the owners of the SP also had interests in the oil industry. The final reason for the switch to oil in 1905 was the California legislature banning coal after a series of wildfires caused by flying locomotive cinders.