Smithsonian Paleobiology Dept. said:
In the mid-1980s paleontologist Jerry MacDonald brought national recognition to the Robledo Mountains, located northwest of Las Cruces, NM, when he found abundant fossilized trackways of ancient vertebrates and invertebrates. These trackways belong to the Permian Period (299-252 million years ago), tens of millions of years before the dinosaurs, at the end of the Paleozoic Era (542 -252 million years ago). Research conducted by scientists from the New Mexico Museum of Natural History and Science (NMMNHS), in collaboration with researchers from around the world, has proven the Robledo trackways to be one of the most important examples of the life habits of Late Paleozoic terrestrial animals. The fossil record in the Robledo Mountains has given scientists a unique window hundreds of millions of years in the past and because of this it was dedicated as Prehistoric Trackways National Monument (PTNM) in March of 2009.
The PTNM also contains fossils of other types, equally important and of interest to a broad range of scientists. Among these are various remains of fossil plants, studied by scientists from the Smithsonian, University of London and University of California, Berkeley. The most common of these fossils are primitive conifers, some of which are the earliest of their kind yet found.