The Galisteo Formation is an Eocene geologic unit in north-central New Mexico made up chiefly of river-deposited sandstone and mudstone, with lesser conglomerate, freshwater limestone, and sedimentary tuff. Dating to about 42 to 38 million years ago, it records ancient fluvial systems and sediment carried mainly from highlands to the northeast and northwest. Its rocks provide important evidence that Sandia Crest had not yet been uplifted in the Eocene and preserve signs of tectonic movement, including links to uplift in the southern Sangre de Cristo Mountains and the Pajarito Uplift. Though generally sparse in fossils, it has yielded titanotheres, petrified wood, and other mammals.