Sierra NF still needs ya to pick up permits in Prather right? not exactly convenient from VVR... will they write permits at the High Sierra ranger station at Bosillo Creek? I have had the same question about the Dinkey Creek ranger station but haven't had the need yet.
Get a non-whitney permit for Mosquito Flat/Mono Pass for the day you intend to leave.
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Then get a whitney permit for Mono Creek for the day you anticipate reaching the JMT junction.? We don't know your dates, but they appear to be plentiful. Mono Creek is the trailhead for VVR. If you want to be strict about it, exit the trail via the ferry
to VVR, have a burger (or stay the night), then ferry back to the other side of the lake.? The ferry landing is about 1.5 miles from the JMT junction. If needed, there are great campsites across the bridge at the JMT junction, and another good one on the lake,
down slope from the trail, as you approach the landing. There's even a picnic table and bear boxes.