After doing some research, I found that those slugs are called leopard slugs, along with a few other common names. And they are the largest species of slug in the world. The slug was as big around as my thumb, and I don't have small hands. I'm just glad it wasn't in my yard.
Yep! You got it right, leopard slug. I had never seen them until we moved into our house about 11 years ago. We see them in the back yard every year. A couple weeks ago my wife saw about 10 different ones crawling around in the back yard. I think I read some where that they eat other slugs. They can get about 5" long.