I'm with Ben on the one county challenge per state opinion. Having a second (on through 58th) version simply reduces the challenge of the challenge cache.
If you're bent on creating a new challenge cache, you could place a cache in each of the 58 counties and make a challenge cache from that à la Cache Across America. You could even call it the Cache Across California Adventure (CACA for short) and use the acronym as part of the naming convention for each cache! For example, you could use the acronym followed by the county name: CACA Lake, CACA Kings, CACA Del Norte. Or you could put the county name before the acronym: Orange CACA, Imperial CACA, Inyo CACA.