Can you dig into a side hill? If you can't dig, then you have to bury. Temperature stability is achieved at about 10'. That's an awful lot of dirt you have to pile onto the structure, but it can be done.
My understanding is that canned goods shouldn't be stored in a root cellar because of the humidity. Root cellars should be high humidity and canned goods are better in low humidity so as to prevent or at least slow down rust. My plan is to have canned goods in the dryer part under my house and the root cellar area needs to be rodent proof and moister.