In this level you will make your way down to an open area with train tracks and defeat an ambush of horseback riders and a cannon. For a detailed description, see below:
Start walking East and kill everything that moves. There will be a fair amount of enemies to take down so keep an eye on your health if you're the reckless type like I am. When you finally come to an open space you'll see Soapy lying on the train tracks. Walk to him to trigger a cutscene - in this case, an ambush.
If you're playing on Easy feel free to ride around recklessly shooting everyone until they're all dead. If you're playing on a harder difficulty, your best bet is to hide behind the boulder on the hill and pick off enemies one by one as they cross your path. Be careful to stay behind the boulder because Dutchie has manned the cannon on the train and will hit you hard if you're too exposed.
When the number of enemies on horses has decreased, feel free to lean out and start taking shots at Dutchie on the cannon. I suggest using a sniper rifle and firing at his head, if you can get the shot. Once he's dead, ride out from behind the rock and defeat the few remaining horseback riders to finish the level.