Great Sand Dunes National Park and Preserve
Great Sand Dunes National Park and Preserve is a national park of the United States that conserves an area of large sand dunes on the eastern edge of the San Luis Valley, and an adjacent national preserve in the Sangre de Cristo Range, in south-central Colorado. The park was originally designated Great Sand Dunes National Monument on March 17, 1932, by President Herbert Hoover. The original boundaries protected an area of. A boundary change and redesignation as a national park and preserve was authorized on November 22, 2000, and then established on September 24, 2004. The park encompasses while the preserve protects an additional for a total of. The recreational visitor total was 527,546 in 2019.
The park contains the tallest sand dunes in North America, up to tall. The dunes cover an area of about and are estimated to contain over of sand. Sediments from the surrounding mountains filled the valley over geologic time periods. After lakes within the valley receded, exposed sand was blown by the predominant southwest winds toward the Sangre de Cristos, eventually forming the dune field over an estimated tens of thousands of years. The four primary components of the Great Sand Dunes system are the mountain watershed, the dune field, the sand sheet, and the sabkha. Ecosystems within the mountain watershed include alpine tundra, subalpine forests, montane woodlands, and riparian zones.
Evidence of human habitation in the San Luis Valley dates back about 11,000 years. The first historic peoples to inhabit the area were the Southern Ute Tribe; Apaches and Navajo also have cultural connections in the area. In the late 17th century, Diego de Vargas, a Spanish governor of Santa Fe de Nuevo México, became the first European on record to enter the San Luis Valley. Juan Bautista de Anza, Zebulon Pike, John C. Frémont, and John Gunnison all traveled through and explored parts of the region in the 18th and 19th centuries. The explorers were soon followed by settlers who ranched, farmed, and mined in the valley starting in the late 19th century. The park was first established as a national monument in 1932 to protect it from gold mining and the potential of a concrete manufacturing business.
Visitors must walk across the wide and shallow Medano Creek to reach the dunes in spring and summer. The creek typically has a peak flow from late May to early June. From July to April, it is usually no more than a few inches deep, if there is any water at all. Hiking is permitted throughout the dunes with the warning that the sand surface temperature may reach in summer. Sandboarding and sandsledding are popular activities, both done on specially designed equipment that can be rented just outside the park entrance or in Alamosa. Visitors with street-legal four-wheel drive vehicles may continue past the end of the park's main road to Medano Pass on of unpaved road, crossing the stream bed of Medano Creek nine times and traversing of deep sand. Hunting is permitted in the preserve in the autumn, but prohibited within national park boundaries at all times. The preserve encompasses nearly all of the mountainous areas north and east of the dune field, up to the ridgeline of the Sangre de Cristos.
History
Native people
The oldest evidence of humans in the area dates back about 11,000 years. Some of the first people to enter the San Luis Valley and the Great Sand Dunes area were nomadic hunter-gatherers whose connection to the area centered around the herds of mammoths and prehistoric bison. They were Stone Age people who hunted with large stone spears or dart points now identified as Clovis and Folsom points. These people only stayed when hunting and plant gathering was good, and avoided the region during times of drought and scarcity.Modern American Indian tribes were familiar with the area when Spaniards first arrived in the 17th century. The traditional Ute phrase for the Great Sand Dunes is Saa waap maa nache. Jicarilla Apaches settled in northern New Mexico and called the dunes Sei-anyedi. Blanca Peak, just southeast of the dunes, is one of the four sacred mountains of the Navajo, who call it Sisnaajini. These various tribes collected the inner layers of bark from ponderosa pine trees for use as food and medicine. The people from the Tewa/Tiwa-speaking pueblos along the Rio Grande remember a traditional site of great importance located in the valley near the dunes: the lake through which their people emerged into the present world. They call the lake Sip'ophe, which is thought to be the springs or lakes immediately west of the dune field.
Settler exploration
In 1694, Don Diego de Vargas became the first European known to have entered the San Luis Valley, although herders and hunters from the Spanish colonies in present-day northern New Mexico probably entered the valley as early as 1598. De Vargas and his men hunted a herd of 500 bison in the southern part of the valley before returning to Santa Fe. In 1776, Juan Bautista de Anza and an entourage of men and livestock probably passed near the dunes as they returned from a punitive raid against a group of Comanches. At this time, the valley was a travel route between the High Plains and Santa Fe for Comanches, Utes, and Spanish soldiers. The dunes were likely a visible landmark for travelers along the trail.The first known writings about Great Sand Dunes appear in Zebulon Pike's journals of 1807. As Lewis and Clark's expedition was returning east, U.S. Army Lt. Pike was commissioned to explore as far west as the Arkansas and Red Rivers. By the end of November 1806, Pike and his men had reached the site of today's Pueblo, Colorado. Still pushing southwest, and confused about the location of the Arkansas River, Pike crossed the Sangre de Cristos just above the Great Sand Dunes.
In 1848, John C. Frémont was hired to find a railroad route from St. Louis to California. He crossed the Sangre de Cristos into the San Luis Valley in winter, courting disaster but proving that a winter crossing of this range was possible. He was followed in 1853 by Captain John Gunnison of the Corps of Topographical Engineers. Gunnison's party crossed the dune field on horseback.
19th & 20th century settlement
In the years that followed, the Rockies were gradually explored, treaties were signed and broken with resident tribes, and people with widely differing goals entered the San Luis Valley from the United States and Mexico. In 1852, Fort Massachusetts was built and then relocated to Fort Garland, about southeast of the Great Sand Dunes, to safeguard travel for settlers following the explorers into the valley. Although many settlers arrived via the trails from Santa Fe or La Veta Pass, several routes over the Sangre de Cristos into the valley were well-known to American Indians and increasingly used by settlers in the late 1800s. Medano Pass, also known as Sand Hill Pass, and Mosca Pass, also called Robidoux's Pass, offered more direct routes from the growing front range cities and dropped into the valley just east of the Great Sand Dunes. Trails were improved into wagon routes and eventually into rough roads. The Mosca Pass Toll Road was developed in the 1870s and stages and the mail route used it regularly until about 1911, when the western portion was damaged in a flash flood. Partially rebuilt at times in the 1930s through the 1950s, the road was repeatedly closed due to flood damage and is now a hiking trail.The Herard family—after whom Mount Herard is named—established a ranch and homestead along Medano Creek in 1875, using the old Medano Pass Road to travel to and from their home. The modern unpaved road follows the old route and is open only to four-wheel drive, and high-clearance vehicles as it passes through deep sand, rises to Medano Pass, and continues east into the Wet Mountain Valley. The Herards grazed and bred cattle in the mountain meadows, raised horses, and established a trout hatchery in the stream. Other families homesteaded near the dunes as well, including the Teofilo Trujillo family whose sheep and cattle ranch in the valley later became part of the Medano–Zapata Ranch, owned by the Nature Conservancy since 1999. The Trujillo's extant homestead and the ruins of a destroyed one were declared a National Historic Landmark in 2004. Frank and Virginia Wellington built a cabin and hand-dug the irrigation ditch that parallels Wellington Ditch Trail located south of the park campground.
Gold and silver rushes occurred around the Rockies after 1853, bringing miners by the thousands into the state and stimulating mining businesses that are still in operation. Numerous small strikes occurred in the mountains around the San Luis Valley. People had frequently speculated that gold might be present in the Great Sand Dunes, and local newspapers ran articles in the 1920s estimating its worth at anywhere from 17 cents/ton to $3/ton. Active placer mining operations sprang up along Medano Creek, and in 1932 the Volcanic Mining Company established a gold mill designed to recover gold from the sand. Although minute quantities of gold were recovered, the technique was too labor-intensive, the stream too seasonal, and the pay-out too small to support any business for long.
Preservation
The idea that the dunes could be destroyed by gold mining or concrete manufacturing alarmed residents of Alamosa and Monte Vista. By the 1920s, the dunes had become a source of pride for local people, and a potential source of tourist dollars for local businesses. Members of the P.E.O. Sisterhood sponsored a bill to Congress asking for national monument status for Great Sand Dunes. Widely supported by local people, the bill was signed into law in 1932 by President Herbert Hoover. Similar support in the late 1990s resulted in the monument's expansion into a national park and preserve in 2000–2004.Geology
The park contains the tallest and widest sand dunes in North America, rising to a maximum height of from the floor of the San Luis Valley on the western base of the Sangre de Cristo Range. The dunes cover an area of about and are estimated to contain over of sand.The creation of the San Luis Valley began when the Sangre de Cristo Range was uplifted in the rotation of a large tectonic plate. The San Juan Mountains to the west of the valley were created through extended and dramatic volcanic activity. The San Luis Valley encompasses the area between the two mountain ranges and is roughly the size of the state of Connecticut. Sediments from both mountain ranges filled the deep chasm of the valley, along with huge amounts of water from melting glaciers and rain. The presence of larger rocks along Medano Creek at the base of the dunes, elsewhere on the valley floor, and in buried deposits indicates that some of the sediment has been washed down in torrential flash floods.
In 2002, geologists discovered lakebed deposits on hills in the southern part of the valley, confirming theories of a huge lake that once covered much of the San Luis Valley floor. The body of water was named Lake Alamosa after the largest town in the valley. Lake Alamosa suddenly receded after it broke through volcanic deposits in the southern end of the valley. The water then drained through the Rio Grande, likely forming the steep Rio Grande Gorge near Taos, New Mexico. Smaller lakes still covered the valley floor, including two broad lakes on the northeastern side of the valley. Large amounts of sediment from the volcanic San Juan Mountains continued to wash down into these lakes, along with some sand from the Sangre de Cristo Range. Climate change later significantly reduced these lakes, leaving behind the sand sheet. Remnants of these lakes still exist in the form of sabkha wetlands.
Sand that was left behind after the lakes receded blew with the predominant southwest winds toward a low curve in the Sangre de Cristo Range. The wind funnels toward three mountain passes—Mosca, Medano, and Music Passes—and the sand accumulates in this natural pocket. The winds blow from the valley floor toward the mountains, but during storms, the winds blow back toward the valley. These opposing wind directions cause the dunes to grow vertically. Two mountain streams—Medano and Sand Creeks—also capture sand from the mountainside of the dune field and carry it around the dunes and back to the valley floor. The creeks then disappear into the sand sheet, and the sand blows back into the dune field. Barchan and transverse dunes form near these creeks. The combination of opposing winds, a huge supply of sand from the valley floor, and the sand-recycling action of the creeks are all part of the reason that these are the tallest dunes in North America.
Sufficient vegetation has grown on the valley floor and there is little sand blowing into the main dune field from the valley; however, small parabolic dunes continue to originate in the sand sheet and migrate across grasslands, joining the main dunefield. Some of these migrating dunes become covered by grasses and shrubs and stop migrating. The dune system is fairly stable as the opposing wind directions balance each other out over time. Also, the main dune field is moist beneath a thin layer of dry surface sand. While the top few inches of sand are blown around during windstorms, the moist sand remains largely in place.
Scientists estimate that Lake Alamosa disappeared about 440,000 years ago, but the dunes themselves apparently originate from sand deposits from later, smaller lakes. A relatively new dating process, optically stimulated luminescence, is still in development. This method takes core samples of sand from deep within a dune and attempts to measure how long quartz grains have been buried in the dark. If the deepest sand deposits can be accurately dated, the age of the dunes could be determined. Samples of sand from deep in the dunes have returned OSL dates varying between a few hundred years to tens of thousands of years old. The oldest dated deposits found so far would have accumulated in the late Pleistocene epoch, during the middle years of the current ice age's third stage.
The dunes contain dark areas which are deposits of magnetite, a mineral that has eroded out of the Sangre de Cristo Range. Magnetite is both attracted to a magnet and can be magnetized to become a magnet itself; it is the most magnetic mineral in nature. Magnetite is an oxide of iron which is heavier than the surrounding particles of sand. When overlying sand is removed by wind, magnetite deposits stay in place and are visible as dark patches in the dune field.