I can't be sure about the dates on some of these photos, and some I'm even guessing to put them in a Great Falls collection, but I've done the best I can, given their arrangement in slide boxes and what slides they were with.
First, here is the lovely pond in the park in downtown Great Falls, in fall and winter:
Here are a couple more winter scenes. One is of the Anaconda smokestack on the river in Great Falls (built in 1908 and demolished in 1982; read about it here), and the other, from another undated, but probably somewhat contemporaneous, box, is of the frozen Missouri river near town: (The photo on the right is of Rainbow Falls, just downstream from town.)
The dated slide in the same box as the smokestack shot was this one, labelled "Sun River Elk herd, Spring, '56." It must have been taken on one of Dad's flights over the Montana countryside, possibly near Great Falls, since the Sun River joins the Missouri near the city:
Another slide of indeterminant location is this one, possibly of the river outside of town:
The following rather enigmatic slides were in a box dated August, 1957. The first three are, I suppose, of Great Falls from a nearby hill. But who are the very typically-'50's-attired couple that appear in two of them?
This final slide might have been taken from the same hill, looking in a different direction, (they were in numerical sequence in the slide box) and it does look like there might be a town down in the valley. But none of these views are familiar to me, so they might have been of a different area altogether.