A Surprising Visitor

This afternoon I went to fill up the watering can from the rain barrel


and came upon this visitor keeping warm in the stone wall under Sarah's window.

Can you see it curled up on the ledge of rock?


Here's a closer view.

 And even closer.  It's not as big as it looks.

I checked back later in the day when the stones were out of the sun and it was gone.

Does anyone know what kind of snake it is?