Geology of the San Luis Valley: What priceless treasures are buried here?

The San Luis Valley and Rio Grande Rift The San Luis Valley is part of the Rio Grande Rift system that extends from central Colorado southward through New Mexico, Texas, and into northern Mexico (Figure 1). The rift began to form about 28 million years ago during the Oligocene Period when a largegraben began to sink along deep bounding faults (Figure 2). Geologic cross-sections through the valley indicate two major half-grabens, including the Baca Graben to the east and the Monte Vista Graben to the west (Figure 2). These half-grabens are filled with some 10,000 to 15,000 feet of Tertiary volcanic rocks (from the San Juan Mountains to the west) Read More …