Stopping rust from spreading!

After lurking for over a year here I'd thought it was about time to be an active member!

Gave my a car a thorough washing this weekend and discovered a few things: 1) clay barring works great, and 2) found rust starting in my drivers side fender There are 2 bolts visible when the door is open that hold the rear of the fender starting to turn that nusty orange color (see attached pic). How can I stop this from spreading!!!

The other pic is just a gratuitous pic showing my clean car!

Thanks!