Entering Town
The first thing you want to do is click on the rock in front of the building on the right-hand side. The rock will come in handy later on. Once it enters your inventory, you can enter the town by clicking on the red arrow.
Beginning
Once inside Yaleville, click the small log located between the saloon and the bank. Enter the hotel by clicking the front door and opening it. Once inside the hotel, click the precious stone located on the front desk and leave the building. When you make it back to the streets of Yaleville, immediately enter the saloon by clicking on the red arrow in the doorway. Pick up the bucket on the side of the piano, and click on the piano keys three times. Once complete, pick up the three bottles found on the bar: whiskey, oil and brandy. Next, exit back to the streets of town and click the red arrow on the right side of the screen.
Middle
Once you've reached the new section of town, take the rock out of your inventory, place it on the colored section of ground and use the oil from your inventory on the handgrip of the well. Use the handgrip to pull up the rope, attach the bucket to the end and lower the rope back into the well via the handgrip. Click the handgrip one last time to pull the rope back up, this time with a full bucket of water on the end. Click the bucket to add it to your inventory and enter the store in the background. Collect the hammer from underneath the cart and the nails on top of the chair. Exit the building and click on the red arrow to the left to go back to the main part of town.
End
After reaching the main section of town, enter the sheriff's building. Close the cell to access the barrel in the corner of the room. Drag the nails from your inventory onto your hammer to combine them, then use them on the barrel itself. Once finished, click the blue button on the right wall to reopen the cell door. Retrieve the tumi knife from the cell and use it on the log in your inventory to turn it into an incomplete slingshot. Exit the building, enter the bank and use the tumi on the skeleton's suspenders. Combine the suspenders with the incomplete slingshot and the precious stone from the hotel to form a loaded slingshot. Exit the building and click the red arrow to the right. Continue all the way to the right until you reach the horse. Give the animal your water bucket and mount the horse to jump across the gap.
Boss Fight
Once you've dismounted the horse, continue to the right and enter the home of Buffalo Yale. Be ready for a confrontation as soon as you enter the hideout, making sure to use your slingshot on Buffalo Yale before he shoots you. You can now collect the treasure you've been after all this time and return the Incan artifacts to Machu Picchu.