Rock River Valley

So this is my first real digital painting that I've ever done, and I feel very proud of the outcome. The thing that took the most time was definitely the river, with all the rocks... so that is why I came up with the title like that.

I think the overall time spent on this had to be around 10+ hours. It is the longest I've ever spent on any work, and I think I will have to try it again.

Resources used:
Flowing Stream to get a reference for the rock/river appearance.
My own cloud pic to get the clouds to look real.
Wacom Bamboo Pen Tablet.
Corel Painter Essentials 3.
Adobe Photoshop Elements 5.0.
I used no resources to look at while making the mountains, which I am surprised at how well they turned out.

Comments Please, I would really like some feedback so I know how to improve for my next digital painting.

Original Resolution: 2560 x 1600
Downloadable Resolution: 1920 x 1200
300 dpi.