To follow up on Paul's comment, in a park like Yosemite, which is overrun in the summer, in winter, above the Valley (which is always crowded), you see hardly anyone and you can camp almost anywhere as long as you are off the road and out of sight. You won't have the Rangers coming along to chase you away. Do get a permit, though-they are free. They just want to know you are out there and have proper gear.

One advantage in Yosemite-free parking at Badger Pass. You put a copy of your pass in your window and if you overstay your time, the Rangers will see your car in the lot and come looking for you.
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