Cheyenne River:

Ahhh, trees. We must be near an oasis, or at least, a river of water.

Aha! So we are! The Cheyenne River to be exact! Quickly hurry past the bridges and the red gunmen in the rivers will submerge back and avoid your character. Who says gunmen can't be pacificists at times?

The barrel concealed behind the trees can be reached by standing still near the tree so that the screen intentionally "bumps" you through and reveals a blue spiral to quickly take out the river gunmen if you're in a more blood thirsty mood. (You can swim in the river, after all.) You can do this "bump" trick again after this screen in the forest area to avoid green gunmen fire.

The two barrels at the end of the bridge before the second, woman, shopkeeper holds a red spiral. At the general store, pick up a horse and the warrant. Things are much less frantic in this stage, so I'll point you to the hidden warrant. Don't bother buying it.