As for the smoke, I suspect some of it is steam. When the UP bought the MP, it inherited a piece of railroad running between Newport, Arkansas and Aurora, Missouri, generally following the course of the White River until it reached this point. As you can see, there is a slight grade, and this is where the rails left the river banks and started the climb through the Ozark Hills, finally leveling out around Branson, Missouri. There were a lot of relatively sharp curves and several tunnels, which required helper engines and a lot of track and tunnel maintenance. The UP didn't really want this piece of railroad, the only attraction was the Arkansas Power & Light generating plant at Newark, Arkansas, about ten miles from Newport.

After a few years of sending unit coal trains down this track, the UP determined they could route around the Ozarks by running down to Little Rock and backtracking to Newport, delivering to AP&L using the last ten miles on this piece of railroad, so they sold the rest to the Missouri & North Arkansas. A siderbar here; The right of way between Aurora and Newport was (for the era) well equipped, with welded rail and automatic detection equipment, which was removed by the UP before the sale to M&NA. I have a photo a the last train before M&NA took over, and it's a train that replaced welded rail with jointed rail.

As for the steam, before the sale to M&NA, the unit coal trains had been routed around this area, leaving only a local based at Cotter. There were a few small industries to switch, mostly feed for the local turkey farms, and some plastic pellet shipments for Baxter Labs. This required one crew, and a pair of GP38-2's were left in Cotter for this purpose. The yard in Cotter was located next to the White River, and in earlier times, it would often be under water during spring floods. There was a lot of humidity from the river, and in warm weather, the locomotives would be shut down during the evening. The crew would arrive in the morning and spend about an hour or so getting their lineup, the diesels would be started and left idling. When the crew went to work, the engineer "wiped the throttle", blowing the White River and a variety of combustion problems out of his exhaust manifold. Seen here shoving two empty pellet hoppers up the hill, he will stop short of the grade crossing around the bend, cut off and run back down the hill. A switch will be thrown, the empties will coast down the hill behind the locomotives, and be routed on an adjacent track so they be be on the other end of the locomotives. The local would then assemble his train and be off up the hill to do his day's work, returning to Cotter later the same day.