Can't start Pouring Forth Oil mission

[Bombastulin]

I completed Spines of America quite some time ago, but have not been able to start another story mission since. I have been back to camp and talked to John Marsden a good 20 times, over a period of a month or two, as at first I thought you just had to wait some period of time for him to "get better." I've explored 3/4 of the map, have hundreds of dollars, upgraded gun & horse, but all Marsden has for me is small talk.

I really have no idea what to do or why it's not triggering. Any tips?

[dIV4r]

I am really not sure why it isn't working for you. I can't think of anything you have to do special for this mission to start. 

Do you have an open save file you can save to? Sometimes that fixes issues in the game for whatever reason.

[Tater]

If on Xbox, try tapping left on the pad to see if there is something there you missed? Just a guess here.

[SNAK3S]

You either missed something or the save file is glitched, the only two things I could think of. I am not sure what could be missing but you can check like Tater mentioned.