Yesterday, these frogs were quite common in the woods along the Monocacy River near Frederick, Maryland. The adults were under logs and tree bark on the ground, while smaller ones (probably the same species) were hopping around.
Here is another one.
I am identifying them as the eastern American toad (Bufo americanus). According to White & White (Amphibians and Reptiles of Delmarva, 2002), that species differs from the similar Fowler's toad in having the "cranial crests not touching parotoid glands or connected by a short spur". The arrow in the picture below is pointing at the spur connecting the cranial crest behind the right eye to the swollen parotoid gland.
Here is the book about frogs and other amphibians: G. Kingsley Noble's The Biology of the Amphibia, originally published in 1931; this is the 1954 Dover edition.
I bought it at the used bookstore for $2 a few days ago. The previous owner was Wolfgang P. J. Dittus. Does anybody know who he was? Not that I intend to return the book to him. Obviously, he didn't want it or need it anymore. In fact, the book is so clean and neat that he may have never used it.
Now, notice how puffy the frogs were when I photographed them. This is what Noble said in his book about this behavior, which is common to many species of frogs: "The inflation increases the size of the body and removes all wrinkles from the skin. Smooth, swollen frogs are both difficult to seize and difficult to swallow." Nice behavioral adaptation that presumably serves as a defense mechanism against frog swallowing predators, snakes, for example. Their habit of remaining motionless—even in the presence of a nearby human finger providing a scale—is undoubtedly another behavioral adaptation.