I have seen the picture of 485 in the pit...not a pretty sight. Evidently, just like William said the engine break was not set properly and there was just enough steam leaking through to cause the engine to 'creep' forward. Of course when over half of the engine went over the edge of the pit, BOOM, And those things weigh about 120K pounds, just the engine. I don't remember where I saw the picture...I don't think I have it...
How deep was the pit at Salida. I am going to think it was about 4-5 feet right on the edge....