What Kind of Clouds Are These?

Driving home one afternoon last week I came across some unusual cloud formations to the north and west.  Actually it appeared there were two sets of clouds.

This is a reflection of an unstable weather pattern.  The darker set looked more like a Portuguese Man of War floating above Snake River Canyon.  Looking closely at the bottom of these clouds it appears they’ve grown tentacles.

I’m not a meteorologist even though sometimes I play weather man on radio (and previously on TV).  Perhaps some of you can tell me why we were seeing the different types of clouds and exactly why some have the tails hanging from the bottoms.  Anyone with a good explanation?