Maryland does not tax a non-resident's income the source of which is "services performed outside this State" or "a business, occupation, profession, or trade that is carried on wholly outside this State."
See sections (C)(1)(b) and (C)(1)(c) of Maryland Statutes. http://www.dsd.state.md.us/comar/comarhtml/03/03.04.02.06.htm
Therefore, as long as you never actually (physically) work within Maryland, your work income is not taxable by MD, and you need not file a non-resident MD return so long as you have no non-work income from MD, such as rental income from a property located in MD.
Finally, you should file MD Form MW507 with your employer, advising them that you are exempt from MD withholding under exception 3(b). https://forms.marylandtaxes.gov/current_forms/mw507.pdf
Your income, of course, is entirely taxable by your home state of CA.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
