On this filter mask, activate the Brush Tool (B) and select a soft round one with black color. Use this brush to erase the foreground and midground.

Step 3

Go to Layer > New Adjustment Layer > Hue/Saturation and set it as Clipping Mask. Reduce the Saturation values to -91:

Step 4

Open the landscape 3 image and use the Rectangular Marquee Tool (M)  to select the lower part of the image to add to the ground of the working document.

Click the second icon at the bottom of the Layers panel to add a mask to this layer. Use a soft black brush to remove the rock part and most of the foreground.

Step 5

Make a Hue/Saturation adjustment layer and bring the Saturation settings to -87 to blend the new ground part with the existing one.