The prairies are far from being flat. In fact, CN and CP used more pusher service engines, steam and diesel, in Manitoba and Saskatchewan than they did in the mountains of Alberta and British Columbia. And even Moose Jaw is in a wide valley just discernable when looking at the topography in the photo below.

The dynamic brakes howl and smoke and heat fill the air over westbound freights straining against gravity as they drive down into the Yard in Moose Jaw. The crews I spoke to in those days said it could get away from you quite easy because the yard limit was immediately under a CN branch line, over a small bridge and Hwy 2 right and at the foot of ‘the hill.’

Google 50* 23’17.28”N and 105* 31’46.08” W and check it out.