In William Kuebler Jr.'s book ' The Vista - Dome North Coast Limited ', there is a interesting section on the 1962 Granite Lake wreck. Per the text, the train was traveling 75 - 80 MPH approaching a curve posted for 30 MPH. The speed tape was damaged by the water, and does not show the train's speed at the curve. However it shows that the engineer, recently promoted to the NCL, had been speeding earlier in the run from Paradise, MT. Apparently he had bragged to other engineers that he intended to beat the running time record on this district. More curious is evidence suggesting the fireman was actually running the train at the time of the wreck.
Even more curious is the possibility of mechanical issues with the train's electro - pneumatic braking system. This system had given much trouble in the past, especially in harsh winter weather conditions such as the NCL experienced. Several engineers on this very train's earlier segments complained about poor braking. Although Northern Pacific never admitted to any issues with the electro - pneumatic brake system used on the NCL, the railroad removed the system from use only 2 months later. As stated above and in the book, the I.C.C. never made a definite determination as to the cause of the wreck.
Interest timing on this question, as the wreck happened 49 years ago this week, on March 2nd, 1962.