Please help translate Government to English

I have been reading a 1978 Forest Service timber sale cultural resource inventory report that contains information about the Sumpter Valley Ry. and its logging spurs, including RoW locations and descriptions of any items found related to the RR. I was hoping somebody on this site who is familiar with the FS could help me figure out what they are trying to describe. First, multiple reports of "Rail Clamps" being found. Any ideas? They don't mean fish plate / joint bars, as later those are described as "rail unions." Second, there were five items found described as "Car wheel chock, bolted to RR ties, iron, 40 cm overall." The only thing I can picture is a modern wheel chock, and I nor any of the multiple people I have talked to at the SVRy think they used anything like them the woods. So what could they be?