Does general contractor have to provide list of subcontractors so the Owner can verify subcontractors are being paid?

The GC is only obligated to give you what his contract says he'll give you. Many GCs don't want to give up their subs because owners try to steal them and cut the GC out of his deal. If this is residential, you have a fairly airtight defense in that you've paid the GC and he's giving you lien releases. Even if there were a surprise lien, which is probably unlikely, the dispute would likely be short lived. It also matters how reputable your GC is. 

I agree with the previous answer. Your contract will specify whether you are entitled to a list of his subcontractors and/or whether you are entitled to audit the GC's books. 

If using the AIA or Consensus document contract forms, the contracts contain provisions requiring disclosure of the subcontractors and suppliers to the project owner and professional (such as the architect and construction manager). Under Colorado law, any funds paid on construction projects are trust funds (C.R.S. Section 38-22-127) and so a demand from the owner to the contractor under the State statute requesting a full disclosure of all subcontractors and suppliers (and an accounting for funds paid) is a good place to go if the contract in not explicit.