Both SDSU and CSUSM use a point system for admission, but the points are assigned differently. For example, SDSU awards points for volunteering and health care work experience, but CSUSM does not.
Application procedures and deadlines depend on what type of program you are applying to. For example, CSUSM has an ABSN program, but SDSU does not. CSUSM's ABSN program does not have a deadline for applying, but both schools
do have deadlines for their undergraduate BSN programs.
CSUSM does not apply an expiration date to courses taken. I'm not sure about SDSU on that one, but nearly all other schools do have some sort of expiration period.
So you really have to calculate your points according to each school's system and see where you stand. Or just spend the money and apply to both and see what happens.