Too Big for your bridges - Leap the broken bridge! - Trophy/Achievement.
After you leave Gizzard Gulch immediately heading away towards your 2nd bounty Filthy Hands Floyd you will come across a broken bridge. Sprint at top speed either on the side of the bridge heading towards Filthy Hands Floyd or heading back to Gizzard Gulch. The Trophy/Achievement will unlock once you leaped passed the bridge on either side. In the past people have said that leaping the broken bridge on the way heading back to Gizzard Gulch gave more success on unlocking this Trophy/Achievement so this way maybe the best way to earn this Trophy/Achievement.