This picture is very nicely done. This is the type of thing I used to use as my desktop backgrounds on my computer.
The range of the blue from left to right really catches my eye.
The 2 things I notice that I think could have made it a little better are the bottom of the clouds seem a little dark to me.
Also the cactus and the landscape I think could have been made to stand out a little more.
They tend to blend into the background where I think a little bit lighter on the clouds behind it could have made for a really awesome silhouette which would have added to this picture.
Overall, I think you did a good job.