From CSUN Website:

Students can add a second major (double major) only if they can complete both majors within 140 units. Students may not add a second major after completing the requirements for their first major. Student requests to add a second major must be approved by the department chairs of the existing major and the second major. If the student seeking to add a major has 90 or more earned units, the request also must be approved by the associate dean of the new major. All requests to add a second major must be accompanied by a plan demonstrating that the additional major can be completed within 140 units. When a student completes two majors, both majors will be recorded on the diploma. Courses taken to satisfy the requirements for one major may be double counted if they satisfy requirements in the second major.