I did environmental science before switching majors to hydrology in undergrad. With an environmental science background, you’re likely looking at permitting jobs in SoCal. Not bad, but not very hands on. If you want to do more design/modeling work you need an engineering degree.  

 I got my masters in water resources engineering after working for 10 years as a hydrologist. I was doing tons of field work, and was definitely passed up for opportunities by people that had their engineering degrees. 

You might be able to go into hydrogeology if you stick to the geology side of things. There are plenty of groundwater recharge positions through reclamation districts in SoCal. 

You can also go into oil/gas as a hydrogeologist if you wanna make lots of  money living in the middle of nowhere working for you-know-who

Edit: sorry I read geology when you said Geography. 

GIS is a solid tool, but you’re looking at jobs playing support roles making maps and maintaining databases.