Holgar, I am just a bit concerned about the cows. When our eyes are pulled to the one cow just to the right of center, it appears as a dark rectangular shape. I wonder if you could clone that one out and place one like the whiteface on the near right. I would like to see a head. I would favor a total cow leaving us no doubt as to what it is. It is a small point and just my preference, but you might try it. Keep the scale correct, too, if you decide to try it.
I think the photo has a nice sense of depth and works well in black and white.
In your photo at Hoover Dam, I see interesting shapes and lines of the buildings and dramatic mountains in the background. But, my main question to you is, what did you want us to see? Why did you single out those structures? What was it about them that interested you. I do not find my self thinking , wow, look at that. I do not see the relevance to their location.
I am asking, "Why did you take the picture?" If it was the buildings, how could you have made their presentation a bit more dramatic for us. Do this make any sense to you? Technically, this is a very good shot. It is the art that is missing for me!