Americana; Appalachian Mountains, by Clyde H. Smith. Portland, Oregon: Graphic Arts Center Publishing Company. $9.95.

Centuries have mellowed the Appalachians, which are among the oldest mountains on earth. They do not possess the craggy peaks or the physical grandeur of the younger Rockies. They are rich, however, in subtler treasures, and photographer Clyde Smith has found quite a few of them.

The gorgeous color photographs on these 10-by-13-inch pages reveal hidden waterfalls tumbling gently from countless rushing streams, cloud-filled valleys that give the Smokies their name, lush ridges of wildflowers on which spring blossoms seem to travel northward.

Smith has spent a lifetime in these mountains, and this volume offers us some of their choicest visual delights.