Yes, this really is a cottonwood tree, mostly submerged in a sand dune. According to monument publications, they routinely survive this sort of treatment so long as a few branches remain exposed to air and sunlight. As the dune moves along, the tree is freed from its sandy prison, and looks like a tree again.
To be fussy, though, the trees popularly called cottonwoods are actually poplars. The predominant subspecies in this area is the Rio Grande Cottonwood, a.k.a. Populus wislizeni.
As usual, click on the above picture to get to the Flickr version of this image — it’ll give you lots of options for resizing and otherwise manipulating the source photo.