Basalt

Yellowstone lake. Our favorite basalt beach. How many days did we spend there..?

The last photo is not very good, but I didn't dare approach closer. A group of six otters were swimming idly along the shore. They went away ... and I went swimming their way ... 

Finding fish bones and heads left on the shore, we realized how fierce fishers they were (obviously gourmet fishers also, disliking the heads!)