There should be civil war relics there. If I were you I would keep quiet locally about this site and don't be showing your finds around because there are too many people who will think that since you have permission to hunt, then it is ok for them and their buddies to hunt and pretty soon you are all kicked off the property. It sounds like a potentially great site that you may be able to hunt for several years if you handle it right.
You should be able to find CW era military buttons and bullets along with RR baggage tage. You'll know the tags because they are usually the size of a dime (give or take) but thicker and have the remains of two wires coming out of one spot on the rim, they will be mostly rusted away. You can carefully clean them and they will have the RR name pressed into the lead, of course they will be oxidized to a white patina like the old minnies and .44s
You'll probably find parasol parts too along with the coinage but man... don't just look for coins at a place like that. Cuff buttons usually come in just above a nickel, like a square tab coat buttons come in a bit higher but usually below a penny and i've seen RR baggage seals come in all over the place.
You need to be digging everything for a while, in different spots too. There will probably be several different outhouse sites to dig and who knows what sort of treasure you may dig if you find outhouses from before 1860... bottles and other trash that has become valuable treasure. You can locate the outhouses by common sense and by using a probe. They would likely have been behind the depot or maybe to the side, but i'd guess in the back and far enough to not smell the place up but not so far that you couldn't get there quickly enough or get too wet in the rain... i'd do some research and see if you can locate a picture of the depot or some account of it in an old paper. Some old newspaper will probably have an old picture. Look for times when maybe a politician came through on the train, there will be a picture and it may show both the depot and the out buildings.
Main thing... keep quiet locally about it... just hunt it and post pics here.
I have a site like that here, well two. One is an old park that used to be a depot. It is open to anyone but most people think that there is nothing there... and there isn't a lot left but I still find baggage tage, carved bullets, buttons, and old coins... they are all pretty well masked though and not a good "dig me" sort of signal. The other place it a private yard that I got permission for several years ago. I have filled several display cases with CW relics, some of them quite nice and rare but over the years I have only taken 4 people there and have been very careful about who they were. I keep most of the relics on display at the office that now is on the property... I hunt it anytime. The owner insists that the relics belong to me so I insist that I display them in his office. He is the city attorney and has opened some other doors for me to hunt other land...
If you don't have relics you might look at buying or borrowing some to check with your machine or... here is a list of TID numbers from my F75 some of which came from the old depot here... http://www.findmall.com/read.php?37,1129819,1129819#msg-1129819
HH,
Julien