Ancient Sand Dunes
Still later in the Triassic Period the Monument became part of a vast desert. Winds blowing from the northwest brought great quantities of fine sand and piled them up into large dunes like those in the Sahara or in Great Sand Dunes National Monument in Colorado. But like all deserts, it was not always dry—occasional rainstorms produced many small lakes and ponds. Some of the sand was washed into these lakes or ponds and settled in level layers. This huge sandpile eventually hardened into the buff and light-red sandstone that we now know as the Wingate. The shapes of the old dunes are indicated by the steep dips of sand layers, called crossbeds, which stand out in sharp contrast to the nearly level layers formed in the lakes and ponds ([fig. 10]).
The spectacular scenery of Colorado National Monument owes its existence largely to the 350-foot cliffs of the Wingate Sandstone ([fig. 6]) and to the desert climate, which allows us to see virtually every foot of the vividly colored rocks and has made possible the creation and preservation of such a wide variety of fantastic sculptures. A wetter climate would have produced a far different and smoother landscape in which most of the rocks and land forms would have been hidden by vegetation.
Eroded remnants of the Wingate form most of the named rock features of the Monument and are shown in many of the photographs. Independence Monument—a towering slab of sandstone that resembles a bridge pier ([fig. 6])—is all that is left of a high narrow wall that once connected the point east of Independence View with the high mesa north of the slab and which once separated the two entrances of Monument Canyon. In a few thousand years this remnant, too, may be gone.
Vertical cliffs and shafts of the Wingate Sandstone endure only where the top of the formation is capped by beds of the next younger rock unit—the Kayenta Formation. The Kayenta is much more resistant to erosion than the Wingate, so even a few feet of the Kayenta, such as the cap on top of Independence Monument, protect the rock beneath. Once this cap has been eroded away, the underlying Wingate weathers into rounded domes, such as the Coke Ovens.
Cold Shivers Point ([fig. 53])—a toadstool shaped cap of sandstone of the Kayenta above a vertical cliff of the Wingate—is perhaps the most aptly titled feature of the Monument.
PETRIFIED SAND DUNES in Wingate Sandstone along old Serpents Trail. Looking north across The Redlands and Grand Valley to the Book Cliffs. Battlement Mesa on right skyline. (Fig. 10)
The Coke Ovens ([fig. 11]) and Squaw Fingers were formed partly because most of the caprock of Kayenta has been weathered away and also because the brittle rocks were cracked along an evenly spaced set of vertical joints. These joints trend northward between the two named features. More rapid weathering along these joints helped form the separate rounded domes or spires between them. Similarly, northwestward-trending vertical joints connect and helped shape Kissing Couple, Pipe Organ, and Sentinal Spire.
THE COKE OVENS, looking north from overlook beneath Artists Point. A set of north-south joints has allowed erosion of the Wingate Sandstone to proceed more rapidly along these zones of weakness and has helped create the four ovens shown. Weathering away of the protective caprock of the overlying Kayenta Formation has produced rounded tops on all but the left-hand shaft, which is still protected by the Kayenta. Note alcoves and arches in cliff of the Wingate beyond, the formation of the one on the right having been aided by removal of the underlying soft Chinle Formation. Bench covered by piñon and juniper above Wingate is resistant thin-bedded Kayenta Formation. Cliff above the bench is the Slick Rock Member of the Entrada Sandstone. The Coke Ovens were named from their resemblance to the beehive-shaped brick ovens formerly used to convert bituminous coal into coke for smelting iron. (Fig. 11)
Many of the cliff walls of the Wingate are vertical, some even overhang, yet in some places the slopes are gentle enough to hold talus and to be climbed ([fig. 12]). Why is this? The answer to this question is given in a later section on “Canyon Cutting.”
Arches or shallow caves weathered out of some cliff faces of the Wingate, particularly where the underlying Chinle Formation has been partly scoured away. Although there are no large caves within the Monument, there are three in a row along the road 3 miles west of the Glade Park Post Office. One of these was inhabited until 1958 ([fig. 5]).
Many of the cliff faces of the Wingate are darkened or blackened by desert varnish—a natural pigment of iron and manganese oxides, silica, and clay.[19]
Dinosaurs left their footprints in the sands of the Wingate in parts of the Colorado Plateau, but no tracks or fossils have yet been found in this formation in or near the Monument.