I've camped in two places, it depends on how much snow they have really. There is a scenic loop right before mammoth, after the town but before the first parking area you cant miss it and you just turn off that road somewhere and find a nice flat area. The other place I've camped is right off the highway and instead of turning left to go to the town of mammoth you take a right and drive up into the hills there. Im not sure how "legal" the camping is but my buddy camped for a month two years in a row in the two different places and never got hassled.
Mammoth scenic loop
second camping area (around this pin drop)
Hope that helps. The mammoth inn isnt too expensive in the spring but I wouldn't expect to pay less than like $100 a night.
Evan Heath Visual
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