The Result of Geologic Coincidences

The mountains that ring this basin contain the gypsum layers that make up the sand dunes today

NPS Photo

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Historical/Interpretive Information/Exhibits

Have you ever felt that things fell into place perfectly for you? For the unusual dunes you see to form, the perfect sequence of geologic events had to occur here. Gypsum, the material that makes up the sand dunes, is among the most common on earth and is widely used as a construction material in drywall, plaster of Paris, and concrete. Despite gypsum being found on all seven continents, this place is worthy of being a National Park because gypsum sand dunes are among the rarest geologic features on earth, with only 3 in the entire world! The process of building this geologic wonder has been a long time in the making. In the mountains to the east or west, you may see lighter layers. This is gypsum! It was deposited 280 million years ago by a shallow inland sea that advanced and receded across the southwest, leaving behind the massive deposits of gypsum that make up the white sand today. Flash forward to 70 million years ago when colliding plate tectonics uplifted the horizontal gypsum layers in a massive mountain building event. Around 20 to 30 million years ago these plate tectonics began to pull apart creating the two separate mountain ranges you see today, the San Andres Mountains in the west and the Sacramento Mountains in the east. In between the mountain ranges where you now stand the earth fell away forming the Tularosa Basin. Finally, the ancient Rio Grande River flowed into the Tularosa Basin between 2 and 3 million years ago bringing with it sediments that eventually blocked any water carrying gypsum from flowing out of the basin. Later in this tour, you’ll explore the modern geologic forces that have sculpted these dunes, but without the perfect series of geologic coincidences to set the stage none of this would be possible.