No. CSU San Marcos, like most colleges and universities, are held to two federal laws, the Drug-Free Schools and Community Act and the Drug-Free Workplace Act. These laws say that in order to receive any federal funding (think work-study, financial aid, and federal research grants), the university must prohibit all illegal drugs. Since marijuana is still illegal under federal law, it remains an illegal substance to possess, sell or use on campus or at university related activities.
Failure to follow federal law would cause the university to jeopardize federal dollars that support students, colleges and programs. Also, CSU San Marcos is governed by policies set by the California State University Chancellor's office. The CSU Chancellor has also recognized the risk of federal funds being cut, and has made clear that marijuana policies are not going to change.
View the CSUSM's Drug-Free Campus Policy