The Cochetopa Hills are a mountain range on the

Continental Divide A continental divide is a drainage divide on a continent such that the drainage basin on one side of the divide feeds into one ocean or sea, and the basin on the other side either feeds into a different ocean or sea, or else is endorheic, not ...

in Saguache County,

Colorado Colorado is a U.S. state, state in the Western United States. It is one of the Mountain states, sharing the Four Corners region with Arizona, New Mexico, and Utah. It is also bordered by Wyoming to the north, Nebraska to the northeast, Kansas ...

, United States. The Cochetopa Hills are a sub-range of the

San Juan Mountains The San Juan Mountains is a high and rugged mountain range in the Rocky Mountains in southwestern Colorado and northwestern New Mexico. The area is highly mineralized (the Colorado Mineral Belt) and figured in the gold and silver mining industry ...

and are located in the

Gunnison National Forest The Gunnison National Forest is a U.S. National Forest covering 1,672,136 acres (2,612.71 sq mi, or 6,766.89 km2) Rio Grande National Forest Rio Grande National Forest is a 1.86 million-acre (7,530 km2) U.S. National Forest located in southwestern Colorado. The forest encompasses the San Luis Valley, which is the world's largest agricultural alpine valley, as well as one of t ...

. The range extends from

Marshall Pass Marshall Pass, elevation , is a mountain pass in the Rocky Mountains of central-southern Colorado, US. It lies in northern Saguache County on the Continental Divide between the Sawatch Range to the north and the Cochetopa Hills to the south. T ...

southwest along the winding crest of the divide to Saguache Park. The high point of the Cochetopa Hills is Long Branch Baldy at an elevation of . The Cochetopa Hills form a notable low-elevation span along the Continental Divide in southern Colorado. The peaks in the adjacent Sawatch Range to the northeast and the San Juan Mountains to the southwest are higher with elevations over . Within the Cochetopa Hills are

Cochetopa Pass Cochetopa Pass is a mountain pass in the Rocky Mountains of south-central Colorado. It lies on the Continental Divide between the city of Gunnison to the northwest and the town of Saguache to the southeast. It also lies on the boundary between ...

(elevation ) and

North Pass North Pass (elevation: ) is a mountain pass over the Continental Divide in Saguache County, Colorado. North Pass, is also known as North Cochetopa Pass. The pass is traversed by Colorado State Highway 114 between Saguache to the southeast and ...

(elevation , which were historically important routes across the divide for Native Americans. ''Cochetopa'' is the

Ute Ute or UTE may refer to: * Ute people, a Native American people of the Great Basin * Ute Indian Tribe of the Uintah and Ouray Reservation, Utah * Ute Mountain Ute Tribe, Colorado, New Mexico, and Utah * Southern Ute Indian Tribe of the Southern ...

word for "gate of buffaloes." Today, the Cochetopa Hills are traversed by one paved road, Colorado Highway 114, which crosses the divide at North Pass.

Geology

The Cochetopa Hills are dominated by

Tertiary Tertiary (from Latin, meaning 'third' or 'of the third degree/order..') may refer to: * Tertiary period, an obsolete geologic period spanning from 66 to 2.6 million years ago * Tertiary (chemistry), a term describing bonding patterns in organic ch ...

volcanic rock Volcanic rocks (often shortened to volcanics in scientific contexts) are rocks formed from lava erupted from a volcano. Like all rock types, the concept of volcanic rock is artificial, and in nature volcanic rocks grade into hypabyssal and me ...

s, including

lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fractu ...

s, ash flow

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

s, and

breccias Breccia ( , ; ) is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a varie ...

. These materials originated from over a dozen volcanoes and multiple eruptions in the

San Juan volcanic field The San Juan volcanic field is part of the San Juan Mountains in southwestern Colorado. It consists mainly of volcanic rocks that form the largest remnant of a major Composite Volcanoes, composite volcanic field that covered most of the southern ...

. The rocks exposed today are from eruptions 35 million years ago to 26 million years ago. After major eruptions emptied the

magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it u ...

below these volcanoes, the overlying rock could collapse and produce a sunken crater called a

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

. Evidence of such calderas are found throughout the San Juan Volcanic Field, including where the Cochetopa Hills occur today. One of the earliest of these volcanoes was the North Pass Caldera, which was active 33 million years ago. Through time, the caldera filled with additional volcanic material ejected from other volcanoes, and subsequently erosion reshaped the landscape making the ancient caldera now difficult to detect. However, just to the north of the Cochetopa Hills is the Cochetopa Caldera, a younger collapsed volcano which was active 27 million years ago. This caldera is better preserved with the

rhyolitic 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 miner ...

Cochetopa Dome rising from the caldera center. Today, the Cochetopa Hills mark the southern rim of the Cochetopa Caldera. Evidence of

glaciation A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...

is present at the highest elevations of the Cochetopa Hills. Glacial

cirque A (; from the Latin word ) is an amphitheatre-like valley formed by Glacier#Erosion, glacial erosion. Alternative names for this landform are corrie (from , meaning a pot or cauldron) and ; ). A cirque may also be a similarly shaped landform a ...

s are located on the northeast and eastern sides of Long Branch Baldy where

tarns A tarn (or corrie loch) is a mountain lake, pond or pool, formed in a cirque (or "corrie") excavated by a glacier. A moraine may form a natural dam below a tarn. Etymology The word is derived from the Old Norse word ''tjörn'' ("a small mou ...

and

glacial deposits image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

are found.

Climate

The Cochetopa Hills' climate is classified as a subarctic climate (Dfc) in the Köppen system, with cold, snowy winters and cool summers. It receives precipitation as snow in winter and as thunderstorms in summer, with June typically being a drier month.

References

External links

* {{Authority control Mountains of Saguache County, Colorado Mountain ranges of Colorado Ranges of the Rocky Mountains San Juan Mountains (Colorado)