John thanks for your notes which are very relevant. But these are not wooden markers. These are concrete. I have seen just this weekend three of them, including one of the ones in the photos I supplied for the group to analize. Well, no one has responded with in-depth forensic accounting of this issue, although the contributions are both appreciated and valued.

We need, I think, to find a copy of the SP manual you are talking about and see if it confirms my findings. Of course, it is possible that you could be correct about culverts--because alot of the culverts were nothing more than a corrugated pipe. But having seen much of the line, I seriously doubt it. There is both no need for that many culverts as well as no culverts.

No, it's likely that G means cattle guard. C could mean culvert. M may mean a branch name. The possibliities are fascinating.

Will look forward to see that manual you speak of.

Thx.
LOL