There are two parts on the final boss. The first part is probably the most difficult. What you do is watch where he goes and once he walks over one of the geysers you have to either throw a dynamite or shoot it with your dynamite bow. Timing is the key for this part and use your mini map also, it really helps.
As for the next part its fairly simple. Go to the left side of and there should be a big rock that you can hide behind where he can't hit you (i think its to the left from where you first start). Make sure you don't go too far back because Magruders men will be behind you. Once you find the spot take out your sniper and snipe his head. That will get him angry and he'll throw his super dynamite at you. Once he throws it up simply go into Quick Draw mode and shoot it. Do this a few times and it will cause the rock on top of him to fall.
As for gold locations: http://video.google.com/videoplay?do...+xbox+360+gold