Excellent post Joe! The only thing I would add is that above 12,000 feet some people might want to think about kicking the SPF factor up to 50. The sun can be incredibly brutal at that elevation, especially reflecting off of granite or snow.
Last year I hiked 3 consecutive days prior to Whitney at 10K' to 12K' feet using SPF 30 with no problem. On Whitney Day I used the same sunscreen and found my arms scorched pretty badly by the time I got back down to Trail Camp around 2:00 in the afternoon. Worst sunburn I've had in years. Also, as Joe mentions, inside the ears and as much of your lower nose/nostrils as possible - both areas were burned pretty badly. I wear a safari-style, wide-brimmed hat while hiking, but I just didn't factor in the reflection power from the Sierra granite - it's like a damn mirror for UV!
Also, when choosing sunglasses for hiking at higher elevations, in addition to the UV protection it's really wise to buy the wrap-around style that are fully shielded on the sides - so no glare or reflected UV sneaks in. The Oakley and Wiley X military-issue sunglasses are great at this, but pricey. You can find similar styles at a third the price that do the same job.
Thanks for the reminder Joe!
