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1. The Great Sand Dunes of
Colorado
How They Came To Be

2. 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)

3. A Long, Long, Time Ago…
In our very own galaxy

4. 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.

5. 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.

6. 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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7. 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.

8. 5-15 Million Years Ago
• Glaciers grew in mountain valleys, some
pouring ice and rock far into the San Luis
Valley.

9. 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

10. 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.

11. The End