Strange Clouds for Skywatch

These peculiar clouds had me running from the front yard to the back yard the other night. (Click the photos to enlarge them).

Here is what I saw over the fence in the back yard looking west.

From the front yard, looking a little further south, the darkening sky was the most delicious shade of blue that I have ever seen. It looked like this:

Running to the back yard once again, I caught the sunset colors on those strange clouds:

I hope that you Skywatchers can tell me the name of these clouds. [Later note: You will see, thanks to QuietPaths in the comments below, that these are mammatus clouds. For more photos of these and other rare cloud formations, go here.]

For clouds of every variety as seen all over the world, be sure to visit Skywatch Friday.