I think you are right if you want to be precise. That is in section 29. There should be a section marker to the east which would be a bit south of the GPAA Joshua Tree.
I'm looking at your corners on a pretty small screen but if I had a large screen we could be more precise but who would have a precise GPS out at the property?
I say if you are going to put the corners in concrete get a survey. If you just want to let people 'know' to be legal then being within 10 feet or so in that area should be good enough. If you want to enforce legal rights for any reason then a survey is the best way to go.