Medical writing jobs in California can be found in pharmaceutical and biotech companies, healthcare communication agencies, medical education companies, and academic institutions. Here are some popular job search websites where you can look for medical writing jobs in California:

1. Indeed.com
2. Glassdoor.com
3. Monster.com
4. ZipRecruiter.com
5. CareerBuilder.com
6. SimplyHired.com

You can search for medical writing jobs in California on these websites by entering relevant search criteria, such as "medical writer," "medical editor," or "scientific writer."

There are several pharmaceutical and biotech companies in California, such as Genentech, Amgen, and Gilead Sciences, that hire medical writers. You can check their websites for job openings or search for them on the job search websites mentioned above.

In addition, there are several healthcare communication agencies and medical education companies in California, such as Ogilvy Health, Precision Medicine Group, and MedThink SciCom, that hire medical writers. You can check their websites for job openings or search for them on the job search websites mentioned above.

Academic institutions in California, such as the University of California system, may also have medical writing positions available. You can check their job boards or search for them on the job search websites mentioned above.