I'm not sure what species this is as I haven't been able to find it yet. I was surprised that it wasn't green like most hornworms, but it appeared healthy. I saw a second one with it a day or two later and both later pupated in my backyard. I'm annoyed with myself that I didn't have the presence of mind to go get a ruler or take a photo of the pupae when I found them.

This critter was about the size of my finger - if I remember right, perhaps 2.5 - 3 inches long? The droppings (upper left of photo) were about the size of nice plump raisins which may help give an idea of the size of the critter that made them. I didn't get to see the adults - they must be huge!