Not all acts of discrimination are legally actionable. Only those based on race, gender, national origin and a few other bases that involve important issues of public policy are legally actionable. Your question does not state any factors that would support a legal claim for unlawful discrimination.
You seem to be relying on a company tradition or custom for moving staff to senior positions when a vacancy is created by resignation. Absent an employment contract or collective bargaining agreement that limited the company's unfettered discretion to follow such unofficial practice only when and if it chose, again there is no legal basis mentioned here for any legal claim of discrimination.
"Discrimination" goes on all the time in all human undertakings. It is no more than choosing differently. So, good employees are treated differently than less good; effective work-place practices are chosen over less-effective; etc. Absent a legally-prohibited basis, discrimination is not unlawful. Taking your question at face value, your employer chose not apply a work-place practice to your situation. And so you quit to go where you would be more valued. All of this is fully consonant with the law of California as it relates to employment.
You may want to re-post your question if you have left out here any facts which might constitute the basis for any UNLAWFUL discrimination.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.
Ms. McCall is correct in all respects, and does a good job in explaining how it is UNLAWFUL discrimination that is actionable.
To strictly answer your question, if it were truly unlawful discrimination (based on such factors as gender, pregnancy, age, disability, national origin, color, creed, religion, or the like), you would have to timely file a charge with the Equal Employment Opportunity Commission or with a state human rights agency. The federal filing deadline is usually 300 days from the date of the discriminatory practice. Most types of unlawful discrimination will require such a filing before a lawsuit can be brought.
But, as Ms. McCall pointed out, there is nothing in your posting that is evocative of unlawful discrimination.
Good luck to you.
Michael S. Haber is a New York attorney. As such, his responses to posted inquiries, such as the one above, are limited to his understanding of law in the jurisdiction in which he practices and not to any other jurisdiction. In addition, no response to any posted inquiry should be deemed to constitute legal advice, nor to constitute the existence of an attorney/client or other contractual or fiduciary relationship, inasmuch as legal advice can only be provided in circumstances in which the attorney is able to ask questions of the person seeking legal advice and to thus gather appropriate information.