Ken,
What you have is a 'bin' to store 'green' sand, which is shoveled into a 'dryer' in that little brick house next to it. Once it is dry, it is pumped via air to either of those sand towers. The one with the 'spider' legs was popular in the 50's - note the side by side sand delivery hoses for either side of a F unit.
Sand arrives in covered hoppers, but usually is 'green' and need to be dried. Very dry/very fine sand is used in the locomotive, and wet sand can clog up the sander nozzles. I have seen small terminals and shortline get bagged dry sand and they either lift the bags up to the sand filler or have a small portable compressor to lift the sand(sort of looks like a 'chipper' with a hose on one end).
As you guessed, some lines have dried sand shipped in covered hoppers as well, and the air equipment is hooked up to the car. One of the problems with this is that the sand gets damp, even in a covered hopper. Many times there is a portable dryer that the sand is run through before it is lifted to the sand tower.
Many years ago, I worked for the CB&Q. They picked up loaded covered hoppers of sand from Bay City Sand of Bay City, WI. Just about any week day the local would have 3-4 company service sand cars parked there for loading/pickup. Even in the 1980's I remember seeing BN cars. I suspect BNSF is loading cars there now.
Jim