This absolutely breathtaking image was captured over Crowley Lake, an artificial reservoir of the Owens River, in California (USA).
These unusual clouds, formally known as altocumulus standing lenticularis, generally form over a mountain or a mountain range. (Due in part to the plethora of moist air droplets and water vapor found there) At high altitudes, the air billowing off from the mountains can be forced upwards, where the moisture will condense to sometimes create the rolling wave-like structure (aligned to the wind direction) seen here.
Apparently, the winds inside the clouds can be rather turbulent, making them unappealing to pilots flying through an area prone to developing these wonders of nature.
See a larger image here.
See: Slideshow of Amazing Storms