Apologies for the delay, my internet has been out until now and I just got back online.
Unfortunately, as an at-will employee, you do not have any right to a job description. Although it is incredibly unfair and unethical for your employer to put you on an improvement plan, when it is impossible for you to ascertain what you were actually doing wrong (without a job description) it is unfortunately legal.
This stems from the employment at-will doctrine, which is codified in California Labor Code Section 2922, and states:
"An employment, having no specified term, may be terminated at
the will of either party on notice to the other. Employment for a
specified term means an employment for a period greater than one
I realize that the above information is not what you wanted to hear, and I sincerely XXXXX XXXXX had better news to give you, but I hope you appreciate a direct and honest answer to your question. It would be unprofessional of me and unfair to you to provide you with anything less.
Please let me know if you have any follow up or clarifying questions.
Thanks and best of luck!