Click in Photoshop on the layer directly underneath the Blue Sky layer (Red rocks or Red rock copy, depending on how many rock correction layers you have) and click on the Create a new fill or adjustment layer icon and select Levels... and in the window that opens click OK.

Remove the mask of this layer by clicking on it, holding down the mouse button and dragging and dropping (A) it onto the Delete layer icon :

 

A new window will open asking you if you want to discard the layer mask, answer by clicking on Discard (delete in Photoshop CS2):

 

Now click on the mask of the Blue Sky layer and hold down the mouse button and drag and drop the mask onto the Add layer mask icon ...

.... and press Ctrl + i (Command + i on the Mac) to invert the mask.

Reminder: In Photoshop CS2 we can duplicate a mask by holding down the Alt key (Option key on the Mac), click on the mask and drag and drop it onto the target layer.

So what have we done? We used the mask of the Blue sky layer, copied it to the Levels 1 layer and inverted it. This means that the levels correction will only affect the opposite selection of the sky, which is... yes, rocks and water.

Double click on the thumbnail of the Levels 1 layer in the layers palette:

 

In the new window that opens, move the black slider towards the right...

...until you've reached the beginning of the histogram (B, next screenshot ). The value (Input Levels) will be 18 (C) and instead of moving the slider you can also enter this value in the corresponding box (C):

Click OK when you're done.

By improving the local contrast in some areas we make the image "pop", stand out more and in some cases it will reduce the noise we're seeing.

Click on the Create a new fill or adjustment layer icon and this time select Curves... and in the window that opens click OK.

Remove the mask of this layer by clicking on it, holding down the mouse button and dragging and dropping (A) it onto the Delete layer icon :

A new window will open asking you if you want to discard the layer mask, answer by clicking on Discard (delete in Photoshop CS2) :

 

Now click on the mask of the Levels 1 layer and hold down the mouse button and drag and drop the mask onto the Add layer mask icon ...

Reminder: In Photoshop CS2 we can duplicate a mask by holding down the Alt key (Option key on the Mac), click on the mask and drag and drop it onto the target layer.

There is no need to invert this mask, since it was already inverted.
Double click on the thumbnail of the Curves 1 layer:

 

Add the 4 points to the curves line and move them into the positions as shown in this screenshot...

... and click OK.
The other option is to download these settings here (right click on the link and select Save target as...).
You can then click on the Load... button in the curves window, select the file curves.acv file that you downloaded and click on Load and OK.

After the curves correction your image should look like this:

 

Let's have a look at the next screenshot to understand the actual purpose of this correction.
The curve at A was raised to make the brighter areas in the image (A) stand out more and curve B was lowered to make the dark areas (B) slightly darker, which also makes the noise in those areas less visible. Both corrections have increased the global contrast of the image and as a result the image even looks sharper.
Important: when you make a correction like this make sure that you avoid to lose important details in the shadows and highlights.