1st one's at that destroyed house in the village
2nd-at the very edge of the bottom of the screen, near the players at the save sphere, only as soon as it makes a little beep, hurry up and dig. Don't wait for it to turn red and beep all the way, you'll just get frustrated.
3rd-just before the first bridge near the waterfall. It should be over to the side somewhere.
4th-go to the intersection just before the beach. Go to the right, and you should be at an area that just cuts off. The last one should be right at the edge somewhere.

The only hard part, is to tell the difference between a 1 and a 7, but, it eventually gets a little easier to tell. After that, just go to that cave, run over to that wall on the right side, and type in the code. You should be on the very top of the waterfall. Run over, and you'll see a chest with the grid inside.

Hope that helps!