Vox has a nice piece on the difficulties faced by Colorado marijuana businesses due to the continued Federal prohibition of marijuana:
Even after legalization, it's still very difficult — and potentially dangerous — to operate a marijuana business in Colorado.
The big problem: pot shops and producers still can't work with banks, which see marijuana as too risky of a business due to federal prohibition. This is true in Colorado, where state law says marijuana is legal but federal law says it's not.
This means marijuana businesses can't take conventional loans, and they have to operate with only cash. And although several levels of government have tried to address the issue, they've had no success so far.
None of this is surprising, but it emphasizes that true legalization requires repeal of the federal ban. State-level legalizations are valuable, partly because they put pressure on the feds, but they are not enough. Remember that during Prohibition, many states (including New York, New Jersey, and Pennsylvania) never banned alcohol, yet the federal prohibition did substantial harm, including in those states.