Can i use my US passport as my form of identification to buy recreational weed here? I do not have a driver licence due to my physical disability. I do have a state ID card though.

I am not sure if they sell "recreational weed" or if it's only medical stuff. But I have never heard of someone refusing a US passport as ID, your calif. ID card also should be accepted pretty much everywhere.

Yes

You could use either

Valid state ID will work and be over 21. Officially legal in California as of yesterday.

You can use your state ID card.

If I were you I would call BPG, and ask them directly what their policies are as they relate to recreational users.