Re: Eastern Sierra's advice needed please.
Not a lot of swimming around Bishop, unfortunately. Some small creeks to splash around in, and you'll find those up most canyons on the Sierra side. Four Jeffrey, for example, up the hill from Bishop. Some sites abut the creek. Some of the USFS campgrounds take reservations.
If you go up to the Mammoth Lakes are you'll find, well the Mammoth Lakes. Kinda cold for swimming, and I think only one allows it, but lots of camping and fishing. And it gets rather crowded. Ditto with Convict Lake.
Nearer Bishop and south you can find some places in the Owens River to take a dip, although it's never appealed to me much. And it's hotter in the floor of Owens Valley. Much further south near Lone Pine is Diaz Lake, which has swimming and camping. But it gets rather hot, but being from AZ it may not be a bother to you. I seem to recall they have hookups there if you need AC power, but I can't recall.
You asked about places on the way up; not sure where you're coming from, but from near Phoenix, Flag or Tucson you usually wouldn't hit NV. Off 40 I'd suggest East Mojave Preserve, and Joshua Tree off 10. Both get up a bit in elevation, so the higher parts can be acceptably cool for camping unless you hit a bit heat wave.
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