This is the risk with at-will employment in CA. The employer could very well decide after two days of you working there that they wanted to let you go -- there's no part of the contract keeping either side from ending things early.
I don't think it's unethical to leave after a short amount of time given the employer has no equivalent expectation.
I don't think it's unethical to leave after a short amount of time given the employer has no equivalent expectation.