It's not obvious from these facts whether you've been discriminated against because of your gender. Has your boss or anyone else made any comments about you being femaie, like "you don't need the money, your husband will support you?"
See an employment lawyer to disclose everything you've expedrienced and observed to get some specific advice.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
You should make a making written request to your employer to explain why your salary is being reduced.
If the explanation is that your salary was reduced because you haven't logged any billable hours "for a few months", that would appear, on its face, to justify a reduction.
If your salary reduction was motivated by your gender, you could pursue a wrongful termination lawsuit.
I would strongly urge you to consult immediately with a litigator skilled in this area of the law.
PLEASE NOTE THAT THIS RESPONSE SHOULD NOT BE CONSTRUED AS A LEGAL OPINION OR ADVISE, AND DOES NOT CREATE AN ATTORNEY-CLIENT RELATIONSHIP. IN ORDER TO RENDER A LEGAL OPINION OR ADVISE, THE RESPONDING ATTORNEY WOULD NEED FAR MORE INFORMATION THAN HAS BEEN PROVIDED, AND WOULD NEED TO BE RETAINED PURSUANT TO A WRITTEN FEE AGREEMENT.
You have an interesting situation. Proving the wage reduction is based in whole or in part on your gender will be hard. All discrimination cases are fact specific. One would need to know how big your company is, in other words how many people it employees, and facts relating to the relationships and interaction between you and the company and the male counterpart. You have the burden of proving a state of mind.
If you have facts which will sustain a case, the attorney should be willing to take the case on a contingency. If he/she won't that is a good sign the lawyer does not believe the case is strong.
You should check out lawyers that litigate employment cases and make sure that you find some that offer to consult with you at no charge. Then, discuss the case with at least two. Be prepared to answer specific questions, eg have the dates, and facts ready.
You may have a claim under California's Equal Pay Act, which can be found at Labor Code section 1197.5 and provides:
"No employer shall pay any individual in the employer's employ at wage rates less than the rates paid to employees of the opposite sex in the same establishment for equal work on jobs the performance of which requires equal skill, effort, and responsibility, and which are performed under similar working conditions, except where the payment is made pursuant to a seniority system, a merit system, a system which measures earnings by quantity or quality of production, or a differential based on any bona fide factor other than sex."
Any employer who violates subdivision California's Equal Pay Act is liable to the employee affected for twice the amount of the underpaid wages plus interest. Equal Pay Act violations can be investigated and remedied by making a complaint to the California Labor Commissioner or by a civil lawsuit in court.
If the male coworker holding a comparable job is also not currently billable but is still receiving a considerably higher salary and there are no other production, merit, seniority, or other lawful reasons for the difference then you may have an Equal Pay Act claim.