If you plan to go into Environmental Law, then Environmental Policy would the best major for law school and even if you are do pursue a law degree, Environmental Policy is a much more marketable degree than Resource Management.
SLO’s Environmental Science and Resource Management major curriculum does include some policy courses but I think UCSD’s Policy track is a stronger program for your goal. Both schools will give you a very good education but you are the one attending the schools for 4 years so you need to find your fit academically/financially and socially.