My dwarves don't haul the stuff lying around into the designated stockpile. Any idea why?
What stuff? What stockpile? Is the stockpile full? Are the dwarves busy? Is the stuff owned by a particular dwarf? Is it marked for a job? Is it claimed by the military?
All kinds of stuff: Quivers, bolts, logs, gems, food. Stuff should be hauled to a custom stockpile, and it isn't full, it is nearly empty. Got 20 to 25 idlers and nothing of that stuff is owned by anyone or used in any jobs, neither is it forbidden.
As mentioned i'd check for stones on the stockpile, they block bins in my experience.
But i had an odd issue in my current fort where a single stone in a doorway just would not be moved for months no matter what i did or how many idlers i had. I had to resort to using dfhack to just destroy it so i could finish my king's quarters.
Sounds like it was claimed for another job.
If you do big construction projects this happens all the time. You tell the game to make 121 tiles of Slate floor, and each of the nearest 121 slates is reserved for a tile of floor. It will not be touched for any purpose beyond being made into a floor. If you happen to suspend construction on those 121 floor tiles you now have 121 immoveable pieces of slate sitting around your fortress. Dump will not work. Forbid will only ensure that when you un-suspend those jobs they still can't happen. Crafters will ignore them. The only way to do anything with those 121 pieces of slate is cancel the floor.
The same thing can happen if you're not doing construction because when a dwarf starts making a rok throne/mug/whatever he claims a piece of rock. If you suspend the job in the middle said piece of rock will be claimed for that job, and the only way to un-claim it is cancel the job.
So I strongly suspect what happened is you suspended a job involving rock, and then got frustrated and destroyed the stone intended for that job before you got around to un-suspending the job.
I'm setting up on a beach atm, so, the underlying soil is sand, but if so, the soil should had been more than just yellow sand. It could had been a mixture of clay, white sand, sand, and whatnot, but it beggars the belief that where my dwarves trampled the grass, the soil is just that. Yellow sand. And it beggars the belief that grass damage just happens to spread radially from the spot where the sand is, as opposed to along traffic paths.
Not to mention, sand is being tracked across terrain that was once claystone, at least, if my memory of the pixels are correct. Since the map hasn't had a glass industry and its in the first year, it can't have been sandbag dumped.
The sand has to be coming from somewhere.
IMO the most probable thing is that the local soil is yellow sand, and the dwarves are merely killing the grass. This would appear to spread radially from your well trafficked areas in the same way a contaminent would because it spreads the same way a contaminent would (by dwarf feet). It should be easy to check, too. [k] always tells you what the soil layer is so, so if you [k] the offending square and it says yellow sand AND claystone.
The second most probable thing is that you're buying bags from the caravan, probably to store seeds or something, and dumping the sand.
Nick