Hi Sherry, I'm not personally familiar (isn't it odd that a native tree that grows over a third of the U.S. isn't known by everyone?) but did find this reference:

"Small native tree or large shrub often found growing near streams. The bark is gray and smooth on older trunks and looks like the muscles on a buff arm, hence another common name "musclewood". Grows 20-30 feet." So you were correct about the older trunks having the characteristic bark.

From Google images, the mature tree does have smooth, muscled slate gray bark.

The link will give you more info about this tree than you perhaps want to know...

Monica

Here is a link that might be useful: U.S. Forest Service

Thanks so much for the link, Monica!
With all the new trees I've planted since the hurricane, the forestry site should come in handy. I don't know why I didn't find it when I Googled carpinus caroliniana.
Thanks again!
Sherry

Are you sure it's not a European Hornbeam? The picture I have in a tree book (Creative Homeowner; Complete Trees and Shrubs) looks like what you're describing.

"Carpinus Betulus"