Rail lines enjoy federal protection, due to their importance in moving heavy freight long distances. (Military strategic, ya know.)
Thus, possession of rail or other rail iron is a felony, unless you have paperwork indicating you got it in a legal manner. The stuff is an easy target by unscrupulous scrappers. That's why most scrap yards won't touch it.
Now, if you could find the legal owner of said property, and fashion up a document describing where and how you got the rail section(s), that the owner could sign, you'd be golden.
I have a 16" piece of worn-out modern rail that I'm fashioning into a hobby-sized anvil, and let me tell you, this is hard stuff. Drilling for my Hardy hole is a bear, and I had to farm it to a machine shop for the flat on the heel. The horn has been all grinder work, and a fair amount of hours at that.
Roger