When mining the combined header of Prime, Region, and Zone, the miner will be able to find Prime, Region, and Zone blocks based on the difficulty requirement of each header. It is expected for Zones to have the lowest difficulty, which gives Zone blocks the lowest block time. Upon finding a block with higher difficulty (i.e Prime or Region), all blocks below the difficulty requirement are also valid. So when the Prime chain is extended, so is the Region and Zone chain of the slice being mined.