First of all, you need to locate the lake. It is at Galbadia where you will find shallow waters [the colour seems a bit lighter.]. Now there is an arc of land that edges into the lake. Just press X and you will see the message below:

It's Obel Lake

Throw a rock
Try humming <-- (this does not work in Disc 1 and 2)
A black shadow rose to the surface

Throw a rock
Try humming again <--
Black Shadow: "...Hello, humans. What a lovely time."
"There's something large there...."

Press X again

Black Shadow: "Hello!"
Black Shadow: "Can doe me a favor please?"

What is it? <---
I don't want to hear it.
Black Shadow: "It's my friend, Mr. Monkey, can you find him for me?"
Black Shadow: "Mr. Monkey should be in a forest somewhere. Keep walking around and I'm sure to find him."

Now you need to find Mr. Monkey... Next examine the lake and choose to "throw a rock" and retreat after you have something like the following message below..

.
.
.
The rock skipped 3 times
You need to get a phrase that says "The rock skipped many many times." You will know why later... Now head to Dollet and you will find a train station near it right. On the extreme left, you will find a forest. [Dollet- Hasberry Plains] and you will have the following message.

There is a monkey

Throw a rock <---
Sing (very funny... hahahahaha!)
You will ALWAYS miss if you picked a stone that skips between 1 ~ 5 times... and you will always get this message..

"Ahh Darn it!" Y-You're just a big loser. I make to skip the rock as many times as I want! So there! Ha-ha! Loser! Dork! Idiot! Your mom wear combat boots"

If you use the rock "The rock skipped many many times."... you will definitely see this message:

"... OUCH!
... D-Darn it
... You're gonna to pay for that!"
The monkey will then throw a rock at you and upon inspecting the rock, you will find some carving on it. "URHAEO"

Now report back to Black Shadow.

You need to talk to the Shadow until he have you the corresponding phrases:

1st rock
Balamb Area <Rinual Shores>

Phrase: "At the beach in Balamb something special washes a shore all times"
Now head to Balamb Town [don't enter it]. Instead search the shore way... There is a special edge-out of sand when the tides are low. Just check that area and you will find the second rock "STSLRM"

2nd rock
That's the rock that you have obtained from Mr Monkey. Anyway, if you can't find him the Shadow will give the following hints:

"If he's not around, perhaps he took a train towards Dollet."
--> that's when you can't find Mr. Monkey...
"Mr. Monkey had a rock like this I think..."
that's the clue for that rock... "URHAEO"

3rd rock
Galbadia Area <Timber- Mandy Beach>

"You'll find something on an island of east of Timber, too."
It's an elevated island where you need enter through Ragnarok. Enter it through Balamb is possible. But will be very hard... Just search along the land and you find the rock, "REAIDR"

4th rock
Galbadia Area <Galbadia- Monterosa Plataeu>

"There's also something on top of a mountain with a lake and cavern."
Just followed the trails of the river and it will lead to a waterfall. Now landed Ragnarok on top of the mountain and search the edge where you will found the waterfall and you will have the following message:

A bird is warming an egg.
Check it <--
Leave it alone
Check the egg out and you will have a fight against 2x Thrustaevis, they are quite simple {Mug: 8x Shear Feathers, 6 AP} and you will found the 4th rock "EASNPD"

Writings on the man-made rock: No. Rock Location Carvings on the rock
1. Balamb rock S T S L R M
2. Mr. Monkey rock U R H A E O
3. Timber rock R E A I D R
4. Lake Cavern rock E A S N P D

Words Build taken from the 4 Rock: MORDRED PLAINS HAS TREASURE Hint: Read from right to left from top to bottom on the carvings.

Okay time to head for the Morded Plains. It is north from the Great Plains of Esthar, behind the mountains. You can find the entrance of Trabia Canyon [where Laguna's 4th Dream Sequence occured there...] Next you need to search it thoroughly.

Just simply press X in Morded Plains Area [they look a bit more brighter...] and you will have the following message: [you can't view them on the world map, instead you will find message boxes instead..]

"There are many multicolored rocks with faces all over the place.."
Press X again then a rock will speak:

The blue-faced rock whispers
"People call us :The Liars Rocks!"
"I don't know were the treasure is..."
It will also gives some hints..

"Some just talk nonsense."
"Some just repeat the same thing."
"Some just say opposite of what we say."
Next press X and you have a couple of speeches from other rocks and they are:

The black-faced rock tell you sternly:
"The treasure is probably at the direction of the North Star"
The white-faced rock tells you coldly
"The treasure is located at the west." or
"The treasure is located at the east." or
"The treasure is located at the north." or
"The treasure is located at the south."
The red-faced rock tells you angrily
"The treasure is to the east." or
"The treasure is to the west." or
"The treasure is to the north." Or
"The treasure is to the south." Or
"The treasure is not here."
As you could figure out, that the black-faced rock is the one that keep on telling you the same thing. However if you attempt to follow the white-faced rock to north and next it will say to the east, to all sort of directions!. Therefore the mostly reliable source of information comes from the red-faced rock! Just watch for its speech and move a step towards it's direction each. Ignore all other messages except for the red-faced rock. The treasure, which is a Three Star item is found in the center of the star... But you must have this message box: " The treasure is not here.", press X again and you will get the treasure. It takes time and patient to solve this mystery. Avoid taking long distances, that's a tip that I could give.

There are still two more spots...

Hint #1
"Take sometime off at Eldbeak Peninsula. I bet its a wonderful place."

[that's located at Trabia, and you will see a small edge out facing Dollet if you view the World Map. It is between the vertical distance between Shumi Village and Balamb Town.]

Eldbeak Peninsula : TRETIMEASUREATMINOFFDEISLE

Break the password up and it will give you the following:
If you take out the words TIME and OFF
TRE - TIME - ASUREATMIN - OFF - DEISLE
You get: TREASURE AT MINDE ISLE. The black-faced rock kept saying the treasure was at the north, but instead the blue rock has mentioned that some of the rocks meant opposite of what they mean. At the lower-left area of Esthar, you will find: MINDE ISLAND! [Isle is a common short found used for "Island"]. Refer to Fig 10.1. Now head there (required the Ragnarok] and search the area and you will find another item, Luck-J Scroll!

Hint #2:
This one I am still searching for. "Take a break at the railway road." I think the treasure could be a draw point. I have just simply follow the train track and search it on the oher side where I find a draw point [Curaga] on West Coast of Esthar. You will also find a man in the Seaside Station. That person also uses Level 7 cards!