I just threw some photos onto the Road Bike forum - Yosemite High Country - Let There Be Photographs and Pain - my recent trip to Yosemite National Park's higher reaches. The core of the bike portion of the trip was my ride from Tuolumne Meadows to the Mobile station above Mono Lake, and back - not bad for someone my age and thus I think worthy of mention here.
One thing I noticed about my trip: I felt some serious pain in my chest - not from my heart - on any incline if I didn't take a long time warming up in a very low gear. And it took much more time to recover from even minimal efforts when I did slow down - it was much different than what it's like for me at sea level. I think my age - 61 - had a significant part of what I felt in Yosemite, and played a part in how long it took me to acclimate to hanging out at 8600 feet.