I climbed North Palisade Mountain this weekend and this monument was at the top. I've searched Google and NGS and can't find any info on it. I suspect it was set and then never measured. I don't need it for a job and therefore it's not important. I was just curious. 
The name of a peak to the north of, and lower than your brass cap gives an indication of the elevation you were at: "Cloudripper".
That's quite a hobby you have. I get plenty of exercise jumping to conclusions, assaulting telemarketers, avoiding bill collectors, watching the clock and similar strenuous activities.
Since it's a Fresno County disk, did you check with (wait for it ) Fresno County?
Since it's not important, I didn't want to bother any agency employees. It's more fun to bother people here. If it really gets on my nerves, I might try that.