The Sangre de Cristo Mountains

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The Sangre de Cristo Mountains are one of the longest mountain chains on Earth. They stretch from Poncha Pass, Colorado, in the north to Glorieta Pass, New Mexico, in the south. There are ten peaks over 14,000′ high in the range, more than two dozen over 13,000′.

Miles and miles of excellent alpine hiking trails through millions of acres of the San Isabel, Rio Grande, Carson, and Santa Fe National Forests.

The Sangre de Cristo’s are fault block mountains with major fault lines running along both the east and west sides of the mountains.

In places, there are also fault lines cutting right through the mountain chain. The mountains were pushed up about 27 million years ago, pretty much as one big chunk of rock.

TOn the west side is the San Luis Valley with the Rio Grande Rift Zone running down the middle. On the southeast side is the Raton Basin with a quiet but still active
volcano field.

On the northeast side are the Wet Mountains and the Front Range, areas of pre-Cambrian rock raised up during the Colorado Orogeny some 1.7 billion years ago.

The Sangre de Cristo’s are fault block mountains with major fault lines running along both the east and west sides of the mountains.

The Blanca Massif is also pre-Cambrian rock while the main body of the Sangres themselves is composed of Permian-Pennsylvanian rock and a mix of igneous intrusions, conglomerates and shale that is only about 250 million years old.

The Sangre de Cristo Mountains (Spanish for “Blood of Christ”) are the southernmost subrange of the Rocky Mountains. They are located in southern

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The name of the mountains may refer to the occasional reddish hues observed during sunrise and sunset, and when alpenglow occurs, especially when the mountains are covered with snow. Although the particular origin of the name is unclear, it has been in use since the early 19th century.

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Most people know that Denver is the Mile High City, that much of the city lies at or near an elevation of 5280 feet. However, geologists believe that Denver and its surroundings didn’t always rest at such lofty elevation. During the Miocene period (between 5.2 & 23.3 million years ago), the North American plate, as it drifted westward, thrust over much of the Pacific Plate. “As [the North American plate] reached the Pacific mid-ocean ridge, huge new forces must have developed, forces great enough to reach the continent’s interior, lifting it up as much as 5000 feet.”

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This event not only raised Denver to its present level, it also stretched the continent to its breaking point. At a pair of deep faults that penetrate all the way through the crust and down to the mantle, the earth’s crust cracked, marking the genesis of the Rio Grande Rift, a massive split in the continent that reaches from the upper Arkansas River Valley all the way into Mexico.

For reasons that are not yet clear, the Colorado Plateau experienced a clockwise torsion, helping to pull the rift’s edges apart and allowing the land within to drop thousands of feet. The land within the rift didn’t fall thousands of feet at once, but rather 5-10 feet at a time over millions of years. (A magnitude-7.3, 1983 earthquake dropped the Thousand Springs Valley west of Borah Peak, Idaho, by nine feet. This event is analogous to the numerous times that the Rio Grande Rift must have subsided.)

The formation of the Rio Grande Rift was key in the creation of several mountain ranges. At the head of the Arkansas, the Sawatch and the Mosquito ranges, formerly a single range, were sundered. Further to the south, the Sangre de Cristo Mountains, the youngest of Colorado’s major mountain ranges, had begun to arise.

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Milwaukee Peak crux

Today when you climb in the Sangre de Cristos, the San Luis Valley is the portion of the Rio Grande Rift that you’ll see. This flat, expansive intermontane valley is the size of Connecticut, its elevation at ground level, its true base is many thousands of feet below.

The major fault on the east side of the valley is the Sangre de Cristo fault. Geologists have determined that rocks found in the Sangre de Cristo Mountains are displaced by nearly four vertical miles from the same type of rocks in the valley.

That’s right, to find the same suite of Precambrian rocks that form the core of the mountains 6-7000 feet above the valley, you’d have to dig 13,000 feet below the valley’s floor. Millions of years of erosion and volcanic activity have filled the valley to its present height with sediments and pyroclastic flows.

The Sangre de Cristo’s beginnings actually predate the Rio Grande Rift, however, so we need to take a quick step back.

During the Laramide Orogeny, the period of uplift that gave rise to most of Colorado’s mountains, the pre-Sangres and pre-San Luis Valley also experienced some uplift. This uplift was anticlinal in nature, the most common method of mountain building in Colorado. The southern section of the Front Range (today we call them the Wet Mountains) was rising concurrently and counteracted the proto-Sangre anticline on its east side, which resulted in the development of thrust faults.

These faults allowed the earth’s crust to relieve stress as basement rock was thrust bodily over the younger sedimentary rock. This occurred at least eight times over, with sedimentary rock squeezed between each layer of basement rock like some octuple-decker sandwich.

Locales on the east side of the range near Comanche Peak are ideal for viewing evidence of this early history of the range. With our uplifted mountain block now in place, we’ve set the stage for the Rio Grande Rift to shake things up.

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Milwaukee Peak crux

The creation of the Rio Grande Rift ushered in a period of earthquakes and volcanics. Amidst this violence, the Sangre de Cristos continued to rise, and their uplift was enhanced by the San Luis Valley’s – and to a lesser extent the Wet Mountain Valley’s – continued subsidence along the fault zones.

Geologists believe that the faults along the Sangre de Cristos are still active due to the shape of its ridges. Whereas the end of ridge will typically erode to a point, many of the ridges on the west side of the Sangres end with a triangular facet, which provides evidence of active faulting.

Additionally, fault scarpsat the northern end of the range tell us that range continues to rise at an average of an inch every one-hundred years. Whether this uplift is currently outpacing erosion is another question, however!

Summing up, although an anticline provided the raw material, the range’s basement-rock core, the Sangre de Cristo Mountains stand proud as Colorado’s only fault-block range.

Without the down dropped valleys to their either side, without the extensive faulting, they wouldn’t be the mountains we know today.

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Anderson Motor Co / Rocky Mountain Offroad Tours

345 West Highway 50; Salida, CO 81201

(719) 539-3088 (719) 221-0757 (719) 539-3088

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