In addition to the import laws, regulations and restrictions in the USA, you are confronted with a unique characteristic of China ... export laws, regulations and restrictions. Unlike most Western countries, where it is remarkably easy to export anything, such is not the situation in China.

To be legal, on your own from this side, you would first need a registered company that also possesses an Export Permit to legally export vehicles. If you are doing it on your own, you would need a WFOE, which requires a notable capital investment and a lot of time, effort and paperwork. A Chinese business registration is much easier. Consult a good lawyer.

Alternately, you can work with the existing Chinese manufacturer, assuming that the manufacturer is already licensed for export. You could then strike an agreement with the manufacturer (or Chinese distributor) to arrange delivery to California. At the USA end, you would likely need to establish an American company (very easy to do). As bikerdoc notes, you would then need to jump through all of the regulatory hoops in the USA concerning the importation of vehicles. There are plenty of regulations concerning road-worthiness for ANY vehicle (including bicycles) that are being imported into the USA for commercial purposes.

Finally, as bikerdoc also noted, if it is worthwhile doing, it is likely that an enterprising Chinese individual is already doing it. Your competitive advantage might be, however, a much better understanding of the US market, given your US hometown knowledge, as well as a much better idea of how and where to market the product. It works both ways - just like a Chinese person has a much better understanding of market nuances in China, Americans have a much better understanding of the US market. I've seen several examples of Chinese persons trying to bring products to Western markets and failing miserably because the Western customer is MUCH different than a Chinese customer.

Due diligence is always a good thing, not least of which is the education you get from learning how to jump through hoops. If the e-bike idea doesn't pan out, perhaps you can see other opportunities with your new-found knowledge.

Good luck!