Okay, did some research on the net... but found nothing.

Where the heck are the sand hatchs on a diesel locomotive? For example, a GP38... are they on the roof, or down low? How many? Front or rear?

On a GP or SD they are usually on top of the nose end and on top of the end of the long hood... you will see a round hatch in both locations, that is your sand box.

Thanks PJ.

So a facility for Geeps would not have a sandtower like this?

Gary, I don't see any reason why you wouldn't have a sand tower like that. The long hoses are needed to reach the hatches, and the sand boxes are high on the locomotives so the sand will flow to the tubes for the sanders. On the alco S-1 through 4's the rear sand box opening was right in front of the windshield over the top of the main generator so the heat would keep the sand dry. Here is a sand tower that was on the Erie at Brier Hill yard in Youngstown.
All the geeps have the sand openings on top and the long hoses would also service most EMD switchers too. It might make more sense if the pipes were parallel with the tracks so the hoses could reach both the front and rear boxes.

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Charlie

In this photo, the one visible sand cover is on top of the short hood, and is a hinged, round cover.
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This discussion of where the sand boxes were located on locomotives makes me think back to my days on the Frankfort and Cincinnati Railroad in the 80s when the train crew was required to sand the engines and not the shop personnel. We'd spot the engine(s) next to the sand house, which as a low concrete block building with nothing in it but the sand drier and a pile of sand. Then one of us would perch ourselves on top of the S-2/S-4 hood while the other two took turns filling and hauling a coal bucket full of sand up a flight of steps and hand it to the man on the engine, who would pour the sand into the filler hatch.

And the sand? Well it wasn't the fine silica sand that railroads use; it was good old Kentucky River sand purchased from a nearby dealer and anything but fine. And just to make things interesting, now and then one of the shop people would shove a cigarette package or other such item into the sand box to stop it up! Fun, fun, fun! What an outfit!

Ed, I had the same thing, but an S-1. I found that if you hauled that sand up there and dumped it in you learned how to be a better engineer because you didn't want to have to use that sand.
Charlie

Gary,
That is indeed a standard sand tower and could be found at any diesel facility. The long hoses facilitated reaching the sandboxes in various locations on different units. On hood units typically up top as discussed, on F units typically down on the side somewhere. The UP had many units with separate sandboxes added on the walkways of the units.
Dave

Thanks everyone for the info. A friend of mine who is building a steam era layout gave me an old Stewart Products "HO Diesel Service Facilities" kit that he had acquired years ago. Kind of jump started me back to the layout, adding details to the service area. All that is needed now is just more free time from work !