this marker looks like it is the center of the section. the NWSE says that it is the North West corner of the South East 1/4. and soforth if it was a 1/4 / 1/4 it would have additional letters stating more about the exact 1/4 / 1/4 you were in. I think that because it states SEC 21 that it is the center of the section if it were a 1/4 1/4 it should say something like the whatever 1/4 of section 21 not just sec 21.
thoughts of a Surveyor Intern
I am a little new to Benchmark hunting. is there like a map program where you can place a way point or "push Pin" where the benchmarks are, so when you go out you can catch the ones in an area with out having to go back and forth.