How the Sand Dunes Came to Be

Friday September 12, 2014
Piñon Flats Campground
Great Sand Dunes National Park and Preserve
Mosca, Colorado

 

 

 

We know fall is definitely here when we find it is 49 degrees in the morning.  But our expensive gas line gives our Cozy World heater the glow we need to warm the place up in short order.

After it warms up a bit as well, we set out on another “walk from the campground” set of trails.  I LOVE when we don’t have to drive to trailheads.

The Dune Trail actually takes you from our campground loop B through loop A and then down to the dunes and along Medano Creek before going back up to the visitor center where we can pick up the Wellington Ditch Trail to come back to the campground at Loop C.   The loop is on this map but you have to look closely below the ‘You are Here’ arrow to the bottom campground loop and the purple dotted trail going off toward the dunes, to the parking area and up to the visitor center.

 

 

This is one of the most beautiful desert flowers I have seen. It was growing just off the trail as it left the campground and had a fence around it for protection.  Just look at that color.

 

 

The trail goes through the scrub area on its way to the dune field.  There are wildflowers galore.  I can only imagine how hot it is here in the summer.

 

 

 

I thought these two were particularly interesting, the first for its flower head and the second for its pea like seed pods.

 

 

 

The National Park and Preserve include the Sangre de Cristo Mountains on the right.

 

 

As we near the dune field, we stop to watch a bluebird flitting around in the rabbit bush.

 

 

 

The park and preserve are made up of several entities.  The dunes are actually in the wilderness area.

 

 

The dunes look close but we still have a long way to go before we come to what remains of the seasonal Medano Creek at the foot of the dunes.

 

 

 

This must have been a big year for the creek since it is still at least somewhat visible.  The length and time that Medano Creek flows greatly depends on the amount of winter snowmelt. In heavy snow years, the creek may flow through July or even throughout the summer. Typically, the creek starts to flow in late March or April, with peak flow in late May. We have been told that when the creek is flowing well, the area may look more like a beach in Florida, complete with people in swimsuits, than a Rocky Mountain stream.

 

 

No swimming today that’s for sure.

 

We walk on down toward the day use area where we find changing rooms just like at the beach.  Men’s on one end and women’s on the other. 

 

 

 

On the information board we find this.  I am always so happy to hear that grizzly bears or mountain lions or wolves live anywhere.  I don’t have to see them for just this knowledge to bring a smile to my face.

 

 

From here the trail climbs up to the visitor center and past some VERY tall yucca plants.

 

 

 

 

 

Another plant I love this is Horsebrush.  The shiny wool shields the plant from direct sun and traps moisture from the surrounding air.

 

 

 

The VC has a great film of course and they also have a number of really excellent exhibits including this topo map which shows the dune field between the Sangre de Cristo mountains on the right and the San Juan Mountains on the left.  There is an educational show on the screen behind which describes how these dunes came to be.

 

 

 

In a nutshell, like many other places we have visited in the west, this place too is the result of volcanic action and plate uplift.

First, the La Garita Caldera erupts.  We are told it is the largest known volcanic explosion in Earth history.  Boy that is a BIG statement.

Through extended and dramatic volcanic activity lava and ash create the rounded San Juan Mountains.

Through the breaking apart and movement (rifting) of large surface plates on Earth's surface, the Sangre de Cristo Mountains are uplifted in the rotation of a large plate. With these two mountain ranges in place, the San Luis Valley was born, covering an area roughly the size of the state of Connecticut.

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 Lake later receded from climate change, and from its water cutting through volcanic deposits in the southern end of the valley. With the southern end of the valley breached, the lake  may have drained through the Rio Grande River, forming the Rio Grande Gorge near Taos, New Mexico.

Smaller lakes still covered the valley floor, including two broad lakes in the northeastern side of the valley. Further climate change significantly reduced these lakes, leaving behind a large sheet of sand geologists call the sand sheet.

Sand that was left behind after these lakes receded blew with the predominant southwest winds toward a low curve in the Sangre de Cristo Mountains. The wind funnels toward three mountain passes there 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 on our side of the dunes and Sand Creek, on the far side of the dunes, also capture sand from the mountain side of the dunefield 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 dunefield.  The creek was definitely disappearing into the sand sheet today.

This 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. There are other dunes in Colorado, and in most western states in the US, but none as tall (750 feet) and none as dramatic. Here giant dunes rise in front of the alpine Sangre de Cristo Mountains, while streams flow across the sand seasonally, making for an unusual and unexpected sight.

And there you have it. All of this is part of the 150,000 acres of the Great Sand Dunes National Park and Preserve

 

 

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Outside the visitor center is the half mile Sand Sheet Loop trail.  We decide to stroll around it before heading back up to the campground. 

Encircling the dunefield like a grassy sea, the sand sheet is one of the major components of the Great Sand Dunes sand deposit.  It is the primary source of sand for the dunefield today.  This trail takes you around the field and identifies the plants and history of the people’s who have visited here.

On the map, we have come in from the Trail to the Dunes, gone to the visitor center and are now back at You Are Here.  When we finish the Sand Sheet Loop we will take the Trial to the Monteville Trailhead which also leads to the Wellington Ditch Trail back to the campground.  A full circle.

 

This post will never end if I do details of the Sand Sheet trail so just know that we suggest you do it before you do any other trails for the information and plant identification. Go to the VC, see the exhibits, do the Sand Sheet Trail and then make your plans to see the park.  That’s our advice.  But I do want to show you just this one plant, the apache plume.  Is that neat or what?

 

 

 

Time to head back.  We cross the road and head UP.

In 1927 the Wellington Family hand dug a ditch for irrigation from Mosca Creek to Buck Creek.  This is a serious uphill challenge.  The ditch can still be seen from the trail we are taking back to the campground. 

 

 

The trail takes us up up from the dunes and the VC.   Great views!

 

 

 

I zoom in on the dunes and the patterns are just spectacular.   They are so beautiful they take my breath away and I have little success at controlling my urge to take their picture.

 

 

The trail is quite varied, dry and rocky in some places.  Treed and grassy in others.

 

 

 

 

We come to a section of the trail where we actually walk through the remains of the Wellington Ditch.

 

 

We find some pinyon pine cones with nuts inside.  We try them.  They are delicious.  We spend some time looking for more.  No wonder they are so expensive.  Trying to get them out of the cone is a real task.

 

 

The only wildlife we’ve seen all day has been the blue bird on our way to the dunes until we are very near the campground.

 

 

We’ve actually arrived back in loop C when we see this piggy with his cheeks absolutely stuffed with pinyon nuts.   I guess he’s a yellow bellied marmot but he sure has a long tail.   Does anyone know if he is or is not?  Look at the length of that tail.

 

 

 

 

Back at the campground we walk by this little number.   Not a full timing rig for sure.   But interesting.

 

 

 

The sun is setting earlier and we almost miss it while finishing up our dinner.

 

 

 

 

 

We close our evening out with a talk by the singing ranger who opens with a pretty darn good rendition of Rocky Mountain High.  His talk is “The Dunes Yesterday…and Today”.  He has historic pictures for the adults, fossils and a mammoth tooth to show the kids, they love it.

 

 

Tomorrow we are going to do it again even though after Sleeping Bear we said that was enough walking up giant sand dunes.  Yup, we’re heading out early to walk up the Big Dune and take a look over the 30 square miles of dune field.  Wish us luck!