I went to Lake Vernon on 7/4 from Hetch Hetchy, having camped at the backpackers camp so I could leave at 7 AM (actually be on the trail, as opposed to having the gate open so I could do the paperwork thing). From Vernon, I went up the XC route recommended in Schaffer to Jack Main, then after camping in Jack Main, did a short XC to Mahan were I camped. Mahan is wonderful! Then, on the return, instead of following the route in Schaffer's book back to Vernon I followed a route I saw David Senesac mention elsewhere. down to Vernon.
The route Schaffer recommended is not fun at the top, lots of Manzanita for the top several hundred yards. Otherwise its just walking, but the manzanita... The route David had suggested was quite good, required careful route selection in places though the joints in the rock seemed to follow a 'zig-zag' pattern that I was able to pick out to avoid anything more than class 2. The route wasn't obvious looking up at it, but now that I've been...its obvious to me.
Vernon is reasonable for swimming in its SW end where I camped the first night. While the rocks on the NE shore look tempting, that's a _terrible_ location for swimming - considering how clear Falls Creek flows above Vernon, the amount and depth of muck in Vernon's NE end is amazing. Falls Creek itself, above Vernon, has lots of nice deep swimming holes, and Mahan was great! Beautiful water.
Lots of bugs - gnats going up from Hetch Hetchy to about 5500', mosquitoes whenever the winds weren't blowing them away (especially at Mahan and along the outlet 'creek'), and plenty of deer flies at Vernon.
Water along the way...
1) The pond at 6240+ above Hetch Hetchy has water but is clearly drying. See pic below.
2) The stream before Beehive is flowing, not a lot, but enough to keep the water nice and cool and delicious.
3) No water is flowing over the falls from Branigan into Vernon.
4) Falls Creek, of course, has water. Not a huge flow, but water.
5) Ardeth's outlet (unmarked on the USGS map) is flowing.
6) Mahan's outlet is barely a trickle - just enough to keep the mosquito ponds along it well-stocked, but not enough to make the water look anything but stagnant.
Some pics...
Pond 6240+:
Falls Creek above Vernon:
Mahan Lake:
View from the ridge south of Mahan:
Andrews Peak, and pond 7640+:
Jack Main Canyon from the Staircase:
More Pics Here