CENOZOIC ERA
The mountains, the plains, the rivers, and the lakes all are transitory features of the landscape, created during the recent part of the Cenozoic Era, and all doomed to destruction in the near future, geologically speaking. Even so, some of the plains and mountains may predate man’s evolution onto the earth scene.
Gone were the late Mesozoic seas; never again during our lifetime nor the lifetime of many future generations will marine waters roll over New Mexico, and sea-spawned creatures rule. For the first two thirds of the Cenozoic, the Paleogene Period (25 to 70 m.y. ago), New Mexico suffered from the dying effects of the great Laramide upheaval of the earth’s crust. Large areas were exposed to the harsh erosion of stream and wind. The landscape looked as parts of southwestern New Mexico do today—tall rugged mountain ranges scattered in isolated patches amid wide gravelly plains. But the climate was more humid, and while no large through rivers are known, local great swamps and lakes lay on the plains in debris-trapping lowlands.
Figure 1. Table of geologic time
| Scale of geologic time in millions of years | |||
|---|---|---|---|
| Era | Rocks | Dominant life | |
| Geologic age | |||
| 70 | CENOZOIC | ||
| Neogene | |||
| Pleistocene | Bandelier volcanic ash, basalts, sand dunes, river gravels, glacial & lake beds. | Man | |
| 1 my | |||
| Pliocene | Volcanic rocks of Mt. Taylor, early Valle Grande & Gila region; Santa Fe, Gila, and Ogallala Fms. | Mammals | |
| 11 my | |||
| Miocene | |||
| 25 my | |||
| Paleogene | |||
| Oligocene | Datil, Espinaso, and other volcanic rocks. | ||
| 40 my | |||
| Eocene | Baca, Animas, Nacimiento, San Jose, Raton, Poison Canyon, Galisteo El Rito, Blanco Basin, & Cub Mountain Fms. | ||
| 60 my | |||
| Paleocene | |||
| 160 | MESOZOIC | ||
| Cretaceous | Upper sandstone, shale, & coal. Mesaverde, Pierre, & Niobrara, Dakota Ss. and Mancos Sh. | Dinosaurs | |
| Volcanic rocks, limestone, sandstone, and conglomerate. | |||
| 135 my | |||
| Jurassic | Morrison Fm., Summerville Fm., Zuni Ss., Todilto Ls. & gypsum, Entrada Ss. | ||
| 180 my | |||
| Triassic | Wingate Ss., Dockum Fm., Chinle Fm., Santa Rosa Ss., Moenkopi Fm. | ||
| 370 | PALEOZOIC | ||
| Permian | Rustler Dolomite; redbeds Castile gypsum, Salado Salt. | Amphibians | |
| Artesia Grp.—Capitan reef San Andres Ls.—Goat Seep reef Glorieta Sandstone Yeso Fm.—Bone Spring Fm. | |||
| Abo Redbeds—Hueco Ls. | |||
| 280 my | |||
| Pennsylvanian | Mostly limestone; beds of shale & sandstone; lenses of gypsum, salt, and coal. | ||
| 310 my | |||
| Mississippian | Helms & Paradise Fms. Rancheria Ls. Lake Valley & Escabrosa Lss. Arroyo Penasco & Tererro Fms. | Fish | |
| 345 my | |||
| Devonian | Percha Shale, Ouray Ls. northern dol., ss, and sh. | ||
| erosion | |||
| 400 my | |||
| Silurian | Fusselman Dolomite | ||
| erosion | |||
| 425 my | |||
| Ordovician | Montoya Dolomite El Paso Limestone Bliss | Invertebrates | |
| 500 my | |||
| Cambrian | Sandstone | ||
| erosion | |||
| 1500+ | |||
| PRECAMBRIAN | quartzite, gneiss, rhyolite, andesite, granite, pegmatite, schist, greenstone. | Simple primitive forms | |
Figure 2. New Mexico during Paleogene time
Scenery in north-central New Mexico ([fig. 2]) may have been similar to today’s, with mountains in the same general areas as the present-day Sangre de Cristo, Nacimiento, San Juan, and Brazos ranges. Coarse-grained gravels were stacked up at the edges of the mountains, but out in the adjoining lowlands, floodplain sands and varicolored lake-bed clays settled. Three low areas were “basins” of deposition where thick masses of sediments accumulated—the Raton and Poison Canyon formations in the Raton Basin near Raton, the Animas, Nacimiento, and San Jose formations in the San Juan Basin north and northwest of Cuba, seen along N.M. Highway 44, with thinner deposits of the El Rito and Blanco Basin formations to the northeast of Cuba, and the Galisteo Formation in the Galisteo Basin south and southwest of Santa Fe. Volcanic rocks, the Espinaso beds, overlie the Galisteo but are not much younger in age. Reddish rocks of the Galisteo Formation crop out along U.S. Highway 85 at La Bajada Hill about twenty miles southwest of Santa Fe. The Sandia Mountains’ area appears to have been a lowland.
Silicified wood, chiefly of pines but with some oak and poplar, is abundant in the Galisteo Formation. Large logs, up to 6 feet in diameter and 135 feet long, have been found. In the great swamps of the Raton Basin, where the climate was much like that of Georgia today, tall reeds, water lilies, fig trees, palm trees, magnolias, and sycamores grew in profusion, and contributed to the thick coal beds now mined there. The early ages of the Cenozoic saw the spectacular rise of the mammals to dominance over reptiles on land; numerous remains of the early mammals are found in the Nacimiento and San Jose formations, including the famous Puerco and Torrejon faunas—as well as many clams, snails, fish, turtles, crocodiles, snakes, and birds.