HHC is legal in California, as the state has not explicitly banned this cannabinoid. However, keep in mind that California changed its laws through Bill AB-45  on the use of THC in hemp-derived products. Food and drinks have to contain less than 0.3% THC.
The state defines “tetrahydrocannabinol” to include delta 8, 9, and 10 and any isomers in the definition. Therefore, California lawmakers could restrict HHC at any time. Still, for now, it remains unregulated.
Most US states don’t have any laws covering HHC. Despite this compound being around for decades, it seems lawmakers haven’t heard of it yet. Because of this, HHC is legal in most but not all US states. Here’s a snapshot of the current state of HHC legality in the United States.