reporter: here s how bitcoin mining works. hundreds of bitcoin transactions, before if pays candy, siage pays hu ma are bunled into a block. computers like these all over the world race to solve a complex math problem. the winner gets to upload that block to the block chain, a vast ledger now more than 700,000 blocks long. a new block is uploaded every ten minutes. mine a blow, and you earn 6.25 bitcoin worth at the moment more than $250,000. this one farm earns about 200 grand every week. and this location is one of seven locations that we built and operated this week. reporter: china was the global bitcoin capital, but last year the communist party cracked down. a lot of it migrated to u.s., and it happened really quickly. as of right now, 35% of the