I have read that it's 10-12% for every 3000 feet in elevation from MSL. Which, for you, is a pretty straight forward calculation.
For others, like me, it requires more maths. I'm at about 1900 ft now, so playing in Utah at 3100, I'd subtract about 7 yards on my yardage. So, half a club, at most.
At least, that's how I figured it when I was down there.
R35
I seem to remember you were about half a club as well.