The "Progress" depot and the "Weed City" Depot may or may not be the same building, but they are in different locations. Weed City was down by the west siding switch.
Weed City lasted much longer than it had any right to. It was built largely out of 1X4's. Every time it was about to collapse, another movie company would come by and prop it up again. Finally the hard winter of 1992-3 dumped enough snow on it to do it in.
When the Indiana Jones gang showed up, they moved the Weed City water tank back from the track, and built a new structure, so it is not the same structure from the late 1960's. The standpipe was built in Hollywood for a reported $50k. It is supported by large ball bearing assemblies so it would spin easily. The plywood tank fell in fairly quickly, but the base and standpipe were built to stand the test of time.