The San Juan Basin is a geologic structural basin located near the Four Corners region of the Southwestern United States. The basin covers 7,500 square miles and resides in northwestern New Mexico, southwestern Colorado, and parts of Utah and Arizona. Specifically, the basin occupies space in the San Juan, Rio Arriba, Sandoval, and McKinley counties in New Mexico, and La Plata and Archuleta counties in Colorado. The basin extends roughly 100 miles (160 km) N-S and 90 miles (140 km) E-W.
Silver mining in Colorado has taken place since the 1860s. In the past, Colorado called itself the Silver State.
The Supai Group is a slope-forming section of red bed deposits found in the Colorado Plateau. The group was laid down during the Pennsylvanian to Lower Permian. Cliff-forming interbeds of sandstone are noticeable throughout the group. The Supai Group is especially exposed throughout the Grand Canyon in northwest Arizona, as well as local regions of southwest Utah, such as the Virgin River valley region. It occurs in Arizona at Chino Point, Sycamore Canyon, and famously at Sedona as parts of Oak Creek Canyon. In the Sedona region, it is overlain by the Hermit Formation, and the colorful Schnebly Hill Formation.
McNulty rhyolite is one of four intrusive, igneous geological formations, the Chalk Mountain nevadite, Lincoln porphyry, McNulty rhyolite and Quail porphyry, described, mapped, and named by S. F. Emmons in 1898 within the Tenmile Mining District of southern Summit County, Colorado. The McNulty rhyolite, which is also known as the McNulty Gulch rhyolite, is described by S. F. Emmons as a fine-grained porphyritic rhyolite that is light gray in color and contains many small white feldspars and locally some small smoky quartz crystals. He mapped it as being exposed as small irregular masses in McNulty Gulch and southward beyond the area of the Tenmile Mining District that was mapped at the time. One exposure above the Railroad Boy tunnel, his location 45 in McNulty Gulch, exhibited small drusy cavities containing little tablets of tridymite. He proposed that this rhyolite was either intruded contemporaneously withy or later than the Chalk Mountain nevadite at the time of eruption. Based on field mapping, the McNulty rhyolite was interpreted to cross-cut and post-date the Lincoln and the Quail porphyries. Later geologic mapping in the Tenmile Mining District eliminated the McNulty rhyolite as a recognized geologic formation.
The Bishop Cap Formation is a geologic formation in the Franklin Mountains of southern New Mexico and western Texas and the Hueco Mountains of western Texas. It preserves fossils dating back to the Moscovian to Kasimovian Ages of the early Pennsylvanian.
The Leadville Limestone is a Mississippian geologic formation in the western United States. In Colorado, the upper part is oolitic limestone, while the lower part is primarily dolomite, and somewhat sandy beds indicate the bottom of the formation.
The Lake Valley Limestone is a geologic formation widely exposed in southwestern New Mexico. It preserves fossils dating back to the lower to middle Mississippian.
The Sandia Formation is a geologic formation in New Mexico, United States. Its fossil assemblage is characteristic of the early Pennsylvanian.
The Arroyo Penasco Group is a group of geological formations exposed in the Nacimiento, Jemez, Sandia, and Sangre de Cristo Mountains of northern New Mexico. It preserves fossils characteristic of the late Mississippian.
The Flechado Formation is a geologic formation in the northern Sangre de Cristo Mountains of New Mexico. It preserves fossils dating back to the early to middle Pennsylvanian.
The Berino Formation is a geologic formation in the Franklin Mountains of southern New Mexico and western Texas. It preserves fossils dating back to the middle Pennsylvanian.
The Madera Group is a group of geologic formations in northern New Mexico. Its fossil assemblage dates the formation to the middle to late Pennsylvanian period.
The Bisbee Group is a geologic group in Arizona, Mexico, and New Mexico. It preserves fossils dating back to the early Cretaceous period.
The geology of Utah, in the western United States, includes rocks formed at the edge of the proto-North American continent during the Precambrian. A shallow marine sedimentary environment covered the region for much of the Paleozoic and Mesozoic, followed by dryland conditions, volcanism, and the formation of the basin and range terrain in the Cenozoic.
The Log Springs Formation is a geologic formation in the Jemez, Nacimiento, and Sandia Mountains of New Mexico. Its age is poorly constrained but is thought to be Namurian.
The Osha Canyon Formation is a geologic formation in the Nacimiento Mountains of New Mexico. It contains fossils characteristic of the Bashkirian stage of the Pennsylvanian period.
The La Tuna Formation is a geologic formation in the Franklin Mountains of southern New Mexico and western Texas and the Hueco Mountains of western Texas. It preserves fossils dating back to the Bashkirian Age of the early Pennsylvanian.
The Rancheria Formation is a geologic formation in the Sacramento and San Andres Mountains of New Mexico, the Franklin Mountains of southern New Mexico and western Texas, and the Hueco Mountains of western Texas. It preserves fossils dating back to the Visean Age of the Mississippian.
The Molas Formation is a geologic formation that is found in the Four Corners region of the United States. Its age is poorly constrained but is thought to be Namurian.
The Canutillo Formation is a geologic formation that is exposed in the Franklin Mountains near El Paso, Texas. The formation is Middle Devonian in age.
