Beside the lake where I live in the West Kootenays in British Columbia

When there's nothing else, there's always Oregon Grape!

Does anyone know what this intriguing thing is? I think it is/was a sea creature, but I have no memory of where I found it. It is as hard as a rock, harder than a shell.

Here's a pic of our sweet little house (3 crones live here) in Canada.