Went hiking yesterday at Cuyamaca Peak (5000-6000ft elev.) yesterday because I have never done hiking at an elevation (WELL, I've done leisurely walks on relatively flat grounds at elevation that I don't really count as hiking) and I figured I should probably figure out how I'd react to elevation BEFORE I reached Peru, i.e. Machu Picchu (~8000ft) and Cuzco (something like 11k ft?). It was 70-75F where I live at around sea level but cold enough at the summit that there was snow in the tree shade and I was extremely glad of my sweater (yes I brought a sweater). I have learned that:

1) I'm a-okay at 6K elevation doing a medium - moderately strenuous trail.
2) My water consumption did not noticeably increase, which sort of freaked out the people I was with who were not used to how little water I normally drank.
3) Cheeses get softer at high elevations. Weird but true. Soft cheeses will get weird and gooey at 6K in sandwiches.
4) UV radiation is indeed a lot more severe at high elevations -- I know this because though I remembered to put on sunscreen before I left I (possibly because I'm right handed) missed a spot on the back of my neck, just behind my left ear, and now I have this 2cm spot that's sunburned while the rest of me is fine. So much for my reputation of being thorough.

It's near the end of wild flower season but there was still a bunch of the little blue flowers that I liked everywhere along with the occasional bunches of lupine and poppies so it's quite nice. The snow was weird though. Really weird.