The San Luis Hills are a group of small

mountain range A mountain range or hill range is a series of mountains or hills arranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment that have arise ...

s in Conejos and Costilla counties in the

San Luis Valley The San Luis Valley is a region in south-central Colorado with a small portion overlapping into New Mexico. The valley is approximately long and wide, extending from the Continental Divide on the northwest rim into New Mexico on the south. It co ...

in southern

Colorado Colorado (, other variants) is a state in the Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of t ...

. The individual mountain ranges that make up the San Luis Hills include the Fairy Hills, the Brownie Hills, the Piñon Hills, and the South Piñon Hills. The San Luis Hills' highest point is Flat Top, elevation

Geographical setting

Each of the separate mountain ranges includes flat-topped mesas and hills, and the ranges trend from the southwest to the northeast. Because the individual hills rise from the floor of the San Luis Valley, which is about in elevation, they appear more as hills than mountains, despite rising to eight or nine thousand feet above sea level. The Hills are all within the

Sangre de Cristo National Heritage Area Sangre de Cristo National Heritage Area is a federally designated National Heritage Area in the south central portion of the U.S. state of Colorado. The heritage area includes the San Luis Valley and portions of the Sangre de Cristo Range. The reg ...

Individual ranges

Fairy Hills

The Fairy Hills lie at . They are north of

Colorado State Highway 142 State Highway 142 (SH 142) is a long state highway in southern Colorado. SH 142's western terminus is at U.S. Route 285 (US 285) near Romeo, and the eastern terminus is at SH 159 in San Luis. Route description SH 142 begins in ...

and west of the

Rio Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...

Conejos County Conejos County is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 7,461. The county seat is the unincorporated community of Conejos. Being 50.7% Hispanic in 2020, Conejos was Colorado's largest Hispa ...

Brownie Hills

The Brownie Hills lie at . They are north of

and east of the

, in

Costilla County Costilla County (Spanish for "rib") is a county located in the U.S. state of Colorado. As of the 2020 census, the population was 3,499. The county seat is San Luis, the oldest continuously occupied town in Colorado. History On July 8, 1694, ...

Piñon Hills

The Piñon Hills lie at . They are south of

and west of the

, in

South Piñon Hills

The South Piñon Hills lie at . As their name indicates, they are south of the Piñon Hills in

, and just north of the

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

border.

Geology

The hills are the exposed parts of an intra-rift horst. They are capped by

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

s of the Hinsdale Formation. The basalt is underlain by

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomi ...

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite. ...

volcanic deposits of the lower Conejos Formation.

Recreation

The public lands in the San Luis Hills are not developed for recreation. However, some informal hiking trails exist, and

mountain climbing Mountaineering or alpinism, is a set of outdoor activities that involves ascending tall mountains. Mountaineering-related activities include traditional outdoor climbing, skiing, and traversing via ferratas. Indoor climbing, sport climbing, a ...

and

bouldering Bouldering is a form of free climbing that is performed on small rock formations or artificial rock walls without the use of ropes or harnesses. While bouldering can be done without any equipment, most climbers use climbing shoes to help sec ...

are possible, especially around the Manassa Dike on south side of Flat Top.

Protected areas

The San Luis Hills Wilderness Study Area occupies a tract of land in the Piñon Hills. The wilderness study area was established in 1980 and is owned by the Bureau of Land Management. In 2016, the Western Rivers Conservancy got funding from the Conservation Alliance to purchase a tract in the Brownie Hills on both sides of the

, some of it adjacent to or overlapping with the Rio Grande Natural Area. The plan is to transfer the land to Costilla County, which will manage it for wildlife habitat, agriculture, and public open space.

References

{{Reflist Mountain ranges of Colorado San Luis Valley of Colorado Mountains of Conejos County, Colorado Mountains of Costilla County, Colorado