For example, to rent a 1 bedroom average apartment in san Francisco now is about $3500 a month.
to rent a 1 bedroom average apartment in Los Angeles of 704 square feet is $2,068. So because of this people raised in California don't want to leave so they will do whatever they have to not to leave the state often. The .com industry and TV and Movie making has a lot to do with high rents in Los Angeles and San Francisco and everywhere along the coast. As you can see Joshua Tree temperatures are mostly above freezing which would make above ground camping possible illegally.
Here are the temperatures for Joshua tree for example: