The Great Sand Dunes of

ColoradoHow They Came To Be

Location, Location, Location!

• Great Sand Dunes National Park and Preserve is located in South-Central Colorado, in eastern Alamosa and Saguache Counties.

• Only a few hours drive from Denver.• Area = 84,997 acres (121.4 miles²)

A Long, Long, Time Ago…

In our very own galaxy

On the 3rd planet from the Sun

Somewhere near present day Colorado

The Dunes were discovered by two unlikely characters

Protocol Droids

Okay, so that’s not REALLY what happened…

60-70 Million Years Ago

• Paleozoic sedimentary rocks were uplifted by the Laramide Orogeny and almost completely eroded in some areas. Continued erosion of Paleozoic rocks revealed metamorphic rocks of the Precambrian, especially on the eastern side of the valley, while much remains to the west. This period of erosion went on for millions of years.

40-50 Million Years Ago

• Following the millions of years of erosion came the deposition of the Blanco Basin Formation, which consisted of mudstones inter-bedded with sand and gravel. The features of the San Luis Valley that are familiar to us today began to form with crustal extension initiated the Rio Grande rift system.

25-40 Million Years Ago

• The initial rifting caused a series of volcanic events, creating the Conejos Formation as well as basaltic flows and ash flow Tuffs, which would lead to the formation of the San Juan Mountains.

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18 Million Years Ago• The Conejos Formation thinned eastward, but continued rifting in the east causing a

system of horsts and grabens. The horsts make up what are now the Sangre de Cristo Mountains, while the dropped grabens make up the San Luis Valley. This process continues to this day. The decline of the valley was more extreme towards the east creating a depositional basin in the San Luis Valley. Sediments accumulated here creating the Santa Fe and Alamosa Formations.

5-15 Million Years Ago

• Glaciers grew in mountain valleys, some pouring ice and rock far into the San Luis Valley.

440,000-12,000 Years Ago

• Many scientists consider the Pleistocene to be the period in which dune formation began in the San Luis Valley. Only about 12,000 years ago, a warming climate melted many glaciers worldwide and signaled the end of the Pleistocene. Large quantities of silt, gravel and sand were carried by rivers and streams into the San Luis Valley

Present Day• Today, the rivers and creeks continue to transport sediment into playa lake systems

which are sources of sediment for dune-forming winds of the San Luis Valley, leaving us with breathtaking views.

The End