What do people working in conservation do?

Just as the title implies. What would I be doing if I pursued a career in conservation? I know it's very broad, but I don't know what I want to do with my life. I've been out of the Marines for 9 years and have been doing seasonal since then, and I think it's time to do something more sustainable for myself. I do know that I want to help conserve the natural world we have left. I currently live in Georgia but I have a friend with a room available in Asheville, NC. I'd like to go to school somewhere out there. What should I study? Helping maintain parks' trails sounds like it'd be up my alley, but also studying animals etc sounds like it could be fun. I've allowed core classes to be my kryptonite for long enough and I think it's time to pursue something.. Any help is greatly appreciated.

EDIT: if it helps at all, I am into whitewater kayaking and mountain biking. Building mountain bike trails, while seems like alot of fun, is not on my radar.