He was using a lot of self harm related language and hung up, ignoring call back attempts. thankfully mentioning which town he was driving into before he hung up, so I called dispatch in that county, then called our home county dispatch where he lives and they were going to send a deputy to check on him.

I have called local dispatch before for the very same reason, and like you I was too far away to do anything.  Later a family member of the individual was very upset with me over "calling the cops" and called me to inform me that the inidivual concerned was not happy about it; I told them thank you and that I would rather have them mad at me than not be here.  The family member informed me that there was no way the individual was capable of it.  As I recall this was during suicide prevention month and I had been seeing and hearing ads to advocate suicide awarness and to get people help.  After the call I got to thinking about the family member that had called worked in the medical field and should have seen the signs, and yet did nothing because they did not feel the individual was capable of it so they ignored the signs.

I lost a friend to suicide years ago and after he died I though about the last couple times I had stopped and visited with him in the 2 weeks prior and how he had engaged is some risky behavior and I said nothing.  I wondered if I had said something about how the situation was dangerous and could have killed him and had let him know at that point that he would be missed if something like that happened if it would have changed his mind and he would still be here today.  Unfortunately we cannot go back in time and change things, but I still wonder to this day if it was a cry for help and I did not see it.  Often being too close can cloud someones judgement on how to handle the information they are given, perhaps they reached out to you because everyone that was closer ignored their cries for help.  IMO you did the right thing.