Hi Karl: I'm not an electrician, but I had the same question with my garage when I lived in S. California, and fortunately, my neighbor was a retired electrician.
According to him, if you run the wire outside of your studs then it must be in conduit (rigid or flexible). If you run it through the studs you can use sheathed electrical cable. Its been 12 years since I did this, but it passed inspection then. Not sure if the electrical code has changed.