From the book ...
Based on evidence found in the San Luis Valley, animals have resided there at least 20,000 years and with human neighbors for at least 12,000 years. During this occupation, the climate of the valley has changed from very wet and cold to a dry desert-like area. As the climate altered, people or cultures and animals also transformed. Many of these changes have been recorded in San Luis Valley Rock Art. Ancient images give us clues to the humans and animals who have occupied or visited this valley.
San Luis Valley Rock Art is divided into three geographic areas; the Northwest Quarter, Southwest Quarterl and Southeast Quarter. Each of these three areas has its own unique images as well as others that are shared.
Over 200 photos show images that are found throughout the San Luis Valley. San Luis Valley Rock Art is the most intense study of Petroglyphs and Pictographs ever published for this portion of southern Colorado.