The mountains in our area are well known for their little "hats" they wear in certain weather conditions. My deceased mother used to look at Mt. Hood or Mt. Adams every time we went to town, and say "oh, look at her pretty hat today!"
Recently I finally discovered that these flat little clouds are called Lenticular formations... and the tall stacks of them are referred to as Altocumulus Lenticularis.
According to a Flickr.com user called glenelg48
"Altocumulus lenticularis. These formations are caused by wave motions in the atmosphere and are frequently seen in mountainous or hilly areas.
They are often called wave clouds. They may be triggered off by hills only a few hundred metres high and may extend downwind for over 100 km. The cloud elements form at the windward edge of the cloud and are carried to the downwind edge where they evaporate, as can be seen here. The cloud as a whole is usually stationary or slow moving."
When I posted these photos on my Flickr.com site, two writers contacted me for permission to use the photos... Cliff Mass from Seattle, a professor of atmospheric sciences at the University of Washington, asked to include some lenticular shots in his upcoming book called "The Weather of the Pacific Northwest"..
Another Flickr user named remolcando, a man from Spain called Federico Martinez, has also requested the use of some Lenticular cloud photos for his upcoming book on Mountain Wave Clouds and Soaring [in gliders]. He tells me these clouds are phenomenal for a glider pilot because of the associated winds.
Other people are absolutely convinced these clouds serve as covers for visitors in Space Ships.... perfect shape behind which can hide a flying saucer.
Whatever the reason for enjoying these lovely and unique formations, I think we all get a little thrill seeing these bizarre circling clouds standing for hours over or beside our local mountains.