The Abajo Mountains, sometimes referred to as the Blue Mountains, is a small mountain range west of

Monticello, Utah Monticello ( ) is a city located in San Juan County, Utah, United States and is the county seat. It is the second most populous city in San Juan County, with a population of 1,972 at the 2010 census. The Monticello area was settled in July 1887 ...

, south of

Canyonlands National Park Canyonlands National Park is an American national park located in southeastern Utah near the town of Moab. The park preserves a colorful landscape eroded into numerous canyons, mesas, and buttes by the Colorado River, the Green River, and their ...

and north of

Blanding, Utah Blanding () is a city in San Juan County, Utah, United States. The population was 3,375 at the 2010 census, making it the most populated city in San Juan County. It was settled in the late 19th century by Mormon settlers, predominantly from the ...

. The mountain range is located within the Manti–La Sal National Forest. The highest point within the range is Abajo Peak at . This mountain range, like both the La Sal Range and

Henry Mountains The Henry Mountains is a mountain range located in the southeastern portion of the U.S. state of Utah that runs in a generally north-south direction, extending over a distance of about . They were named by Almon Thompson in honor of Joseph Henry ...

in the same part of the

Colorado Plateau The Colorado Plateau, also known as the Colorado Plateau Province, is a physiographic and desert region of the Intermontane Plateaus, roughly centered on the Four Corners region of the southwestern United States. This province covers an area o ...

, is formed about igneous intrusions that are relatively resistant to erosion. Some of these intrusions form

laccolith 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 (molten rock) rising through the Earth's crust begins to spread out horizontally, prying apar ...

s emplaced at depths of a few kilometers. The predominant igneous rock is porphyritic

hornblende Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rock ...

diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-sil ...

. Ages of intrusion in the Abajo Mountains fall in the interval from 22 to 29 million years. These mountain ranges are part of the

province west of the greater ranges of the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...

. The laccolith ranges are much younger and have a very different geologic origin. The range was reputedly named by the Spanish in the 1700s, the name "Abajo" meaning "low". Plateau laccoliths NASA

References

Colorado Plateau Mountain ranges of San Juan County, Utah Laccoliths Mountain ranges of Utah Manti-La Sal National Forest {{Utah-geo-stub