I don't think that's right. They buried the weapons by the fence surrounding terminus, not by the railroad tracks. I could be wrong, I believe the markings are something that Morgan is following, a "bread crumb" someone is leaving. The Morgan scene seems like it's shortly after the crew leaves. But you can tell the mud is dry on the terminus sign and the tree marking is fresh, so there's a time lapse between those scenes. could be someone is following the crew...
You might be right. I read that in one of the after show reviews..