I got an unexpected surprised while fiddling around with the rocks I have lining the beds in my garden (a work in progress). Here's what I saw when I flipped over a large one on the corner.
This may also explain where my toads go when they aren't lounging on the porch. They might have holes under other rocks in the garden. I'd better remember to be careful when lifting up rocks to make sure I don't squish any.
After things warm up, I'm going to check under the rock again to see if the frog made it. Hopefully I'll find an empty hole where the frog used to be before it came out of hibernation safely and hopped away.