KCB, the whole area is generally surrounded by higher ground, so it would have been frequently wet. Did you notice the slight descending ditch which borders the reedy area?
The fences, I presume, would have have served to keep wildlife away from the crops (whatever crops were grown there). As for the shells, I have no opinion as to their purpose except that they were probably discarded after being eaten. My guess is that the trash was not dumped there but came from the house that probably once stood on the high ground next to the junipers. As for the railroad ties, they appear to have been used as the base for some sort of shed. The house itself, I am guessing, was made of brick. The bricks would have since been salvaged, for only one remains at the site.
But this is merely my opinion. I am no expert when it comes to intepreting stuff like this,