Geology
Tomichi Dome is a prominent igneous mountain formed during the Tertiary. The predominant rock is rhyolite, but microgranite, breccia, and tuff have been cited as present. Surrounding the mountain, on the valley floor, is Mancos Shale, a Mesozoic sedimentary rock. [6] [7] [8]
Tomchi Dome has been described as an intrusion and also as an extrusive, volcanic feature. As an intrusion, the pluton may have formed when magma was intruded into the Mancos Shale resulting in a laccolith. Given the fine-grained texture of the rock, the laccolith is assumed to have been at a shallow depth and cooled rapidly. Venting may have been associated with the intrusion resulting in the rhyolytic breccia and tuff documented in the vicinity. Shallow rhyolitic plutons southwest of Tomichi Dome, in the San Juan Mountains near Lake City, have also been described as laccoliths. [8] [9] [10]
Alternatively, Tomichi Dome has been described as an extrusive, volcanic feature where the initial eruptions deposited breccia and tuff that is over 670 feet (200 m) thick. A flow or dome of topaz rhyolite overlies the tuff. [8] [11] [12]
Whether plutonic or volcanic, Tomichi Dome is possibly one of a string of igneous structures associated with the Rio Grande Rift, which stretches from Mexico to Colorado. [8] [11]
Rhyolite is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral assemblage is predominantly quartz, sanidine, and plagioclase. It is the extrusive equivalent of granite.
The St. Francois Mountains in southeast Missouri are a mountain range of Precambrian igneous mountains rising over the Ozark Plateau. This range is one of the oldest exposures of igneous rock in North America. The name of the range is spelled out as Saint Francois Mountains in official GNIS sources, but it is sometimes misspelled in use as St. Francis Mountains to match the anglicized pronunciation of both the range and St. Francois County.
The Anahim Volcanic Belt (AVB) is a west–east trending chain of volcanoes and related magmatic features in British Columbia, Canada. It extends from Athlone Island on the Central Coast, running eastward through the strongly uplifted and deeply dissected Coast Mountains to near the community of Nazko on the Interior Plateau. The AVB is delineated as three west-to-east segments that differ in age and structure. A wide variety of igneous rocks with differing compositions occur throughout these segments, comprising landforms such as volcanic cones, volcanic plugs, lava domes, shield volcanoes and intrusions.
A laccolith is a body of intrusive rock with a dome-shaped upper surface and a level base, fed by a conduit from below. A laccolith forms when magma rising through the Earth's crust begins to spread out horizontally, prying apart the host rock strata. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith its dome-like form.
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form intrusions, such as batholiths, dikes, sills, laccoliths, and volcanic necks.
Ute Mountain, also known as Ute Peak or Sleeping Ute Mountain, is a peak within the Ute Mountains, a small mountain range in the southwestern corner of Colorado. It is on the northern edge of the Ute Mountain Ute Tribe Reservation. The Reservation forms the southwestern corner of the state and of Montezuma County.
The Solitario is a large geologic formation in Big Bend Ranch State Park in West Texas. When viewed from above, it suggests an impact crater; though it is actually the eroded remains of a laccolith. The approximate center of the Solitario is located 56.8 km (35.3 mi) east southeast of Presidio, Texas, just west of the line dividing Brewster County, Texas and Presidio County, Texas. The formation covers a circular area of approximately 135 km2 (52 sq mi). The geology of the Solitario is complex. In 1988, the state of Texas purchased the property containing the Solitario and created Big Bend Ranch State Park.
Rainmaker Mountain is the name of a mountain located near Pago Pago, American Samoa on Tutuila Island. Rainmaker Mountain traps rain clouds and gives Pago Pago the highest annual rainfall of any harbor. The average annual rainfall on the mountain is around 200 inches (510 cm). It has a three-pronged summit. Rainmaker Mountain and its base were designated a National Natural Landmark in 1972 due to the slopes’ tropical vegetation.
In geology, an igneous intrusion is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and compositions, illustrated by examples like the Palisades Sill of New York and New Jersey; the Henry Mountains of Utah; the Bushveld Igneous Complex of South Africa; Shiprock in New Mexico; the Ardnamurchan intrusion in Scotland; and the Sierra Nevada Batholith of California.
Mount Lamborn is a mountain summit in the West Elk Mountains range of the Rocky Mountains of North America. The 11,402-foot (3,475 m) peak is located in Gunnison National Forest, 5.9 miles (9.5 km) southeast by south of the Town of Paonia in Delta County, Colorado, United States. The summit of Mount Lamborn is the highest point in Delta County. Together with nearby Landsend Peak to the southwest, it lies at the western edge of the West Elks, rising dramatically nearly 6,000 ft above the valley of the North Fork Gunnison River to the west.
The West Elk Mountains are a high mountain range in the west-central part of the U.S. state of Colorado. They lie primarily within the Gunnison National Forest, and part of the range is protected as the West Elk Wilderness. The range is primarily located in Gunnison County, with small parts in eastern Delta and Montrose counties.
Crested Butte is a prominent mountain summit in the Elk Mountains range of the Rocky Mountains of North America. The 12,168-foot (3,709 m) peak is in Gunnison National Forest, 2.1 miles (3.4 km) northeast by east of the Town of Crested Butte in Gunnison County, Colorado, United States. Ski lifts and runs of the Crested Butte Mountain Resort occupy the north side of the mountain.
The Canadian Cascade Arc, also called the Canadian Cascades, is the Canadian segment of the North American Cascade Volcanic Arc. Located entirely within the Canadian province of British Columbia, it extends from the Cascade Mountains in the south to the Coast Mountains in the north. Specifically, the southern end of the Canadian Cascades begin at the Canada–United States border. However, the specific boundaries of the northern end are not precisely known and the geology in this part of the volcanic arc is poorly understood. It is widely accepted by geologists that the Canadian Cascade Arc extends through the Pacific Ranges of the Coast Mountains. However, others have expressed concern that the volcanic arc possibly extends further north into the Kitimat Ranges, another subdivision of the Coast Mountains, and even as far north as Haida Gwaii.
Needle Rock Natural Area is located at the western edge of the West Elk Mountains of Colorado. The surrounding terrain is characterized by laccolithic mountains flanked by precipitous cliffs, extensive talus aprons, forested mesas, canyons, and spacious, well-watered intermontane basins. Needle Rock is an intrusive plug of monzonite porphyry cropping out 3.5 miles (5.6 km) east-northeast of the Town of Crawford in Delta County, Colorado, United States. With an elevation of 7,797 feet (2,377 m), the towering rock spire stands 800 feet (240 m) tall above the floor of the Smith Fork of the Gunnison River valley. The massive rock feature originated in the Oligocene geological epoch when magma intruded between existing sedimentary rocks as the crown of a buried laccolith or possibly the underlying conduit of a laccolith. Subsequent erosion has exposed the prominent rock formation seen in the natural area today.
West Elk Peak, elevation 13,042 ft (3,975 m), is the highest summit in the West Elk Mountains of Gunnison County, Colorado. The mountain is in the West Elk Wilderness, northwest of Gunnison. The terrain consists mostly of volcanic breccia, known in this area as West Elk Breccia, dated at 35 to 30 million years old.
East Beckwith Mountain is a prominent mountain summit in the West Elk Mountains range of the Rocky Mountains of North America. The 12,441-foot (3,792 m) peak is located in the West Elk Wilderness of Gunnison National Forest, 13.4 miles (21.5 km) west by south of the Town of Crested Butte in Gunnison County, Colorado, United States.
Whetstone Mountain, elevation 12,527 ft (3,818 m), is a summit in the Gunnison National Forest of western Colorado. The mountain is located 3 mi (4.8 km) south of Crested Butte in Gunnison County. Whetstone Mountain is one of several prominent laccoliths found in the West Elk Mountains.
West Beckwith Mountain is a prominent mountain summit in the West Elk Mountains range of the Rocky Mountains of North America. The 12,185-foot (3,714 m) peak is located in the West Elk Wilderness of Gunnison National Forest, about 16.5 miles (26.5 km) southwest of Crested Butte in Gunnison County, Colorado, United States.
Tomichi Pass is a high mountain pass in the Sawatch Range of the Rocky Mountains of Colorado. It is located in Gunnison County and in the Gunnison National Forest. The pass divides the watersheds of Middle Quartz Creek to the north and Tomichi Creek to the south.
