by AlmostThere » Tue Sep 15, 2009 9:35 pm
When you say mid-late May, how late is late? Glacier Point Road often opens in early May, and Tioga has been known to open for the last week/two weeks of May. There will be some snow left and creeks will be running very high, making crossings treacherous.
Not too many trips in Yosemite below 7000' - any backpack of that duration will likely take you above that elevation at some point. Hetch Hetchy trails start to climb before you can camp, and Chilnualna Falls trailhead is below that but quickly goes above 7000'. Most Tioga trailheads are right about 9,000' from the start. Happy Isles will start low and within a few miles go above your limit. If you are concerned about altitude sickness, staying a day or two at moderate (6000-7000) and moving up from there is typically the prescribed preventive measure.