INDEPENDENCE MONUMENT, separating the two entrances of Monument Canyon. Looking north from Grand View; Colorado River, Grand Valley, and Book Cliffs in distance. Roan Cliffs are white cliffs at extreme distance on right skyline. Dark rock flooring canyon is Proterozoic metamorphic rock, red material in slope at base of cliffs is the Chinle Formation, vertical cliffs are Wingate Sandstone, thin protective caprock on top of cliffs is lower sandstone of the resistant Kayenta Formation. The top of Independence Monument is nearly 450 feet above the floor of the canyon. (Fig. 6)

ROCK COLUMN OF COLORADO NATIONAL MONUMENT. 1 foot = 0.305 meter. (Fig. 7)

AGE (millions of years) GEOLOGIC AGE NAME OF ROCK FORMATION KIND OF ROCK AND HOW IT IS SCULPTURED BY EROSION THICKNESS (feet) NAMED FOR OCCURRENCE AT OR NEAR 80 Late Cretaceous Mancos Shale Gray and black shale, and thin beds of sandstone and limestone. Contains sea shells. Eroded from Monument, but underlies Grand Valley and forms lower part of Book Cliffs. 3,800 Mancos, Colo. Dakota Sandstone Coaly shale, sandstone, conglomerate, and lignite coal. Contains plant remains. Forms benches and slopes. Caps highest hill in Monument. 150 Dakota, Nebr. 115 Early Cretaceous Burro Canyon Formation Green siltstone and shale, and sandstone and conglomerate. Forms benches and slopes. Crops out on highest hill in Monument. 60 Burro Canyon San Miguel Co., Colo. EROSIONAL UNCONFORMITY 150 Late Jurassic Morrison Formation Brightly colored siltstone and mudstone, and sandstone and limestone. Contains dinosaur bones and fresh-water shells. Forms slopes and badlands. Lower third with sandstone lenses is Salt Wash Member, upper two thirds is Brushy Basin Member. 600 Morrison, Colo. 170 Middle Jurassic Summerville Formation Brightly colored siltstone and mudstone, and thin sandstones. Forms slopes. 54 Summerville Point San Rafael Swell, Utah Entrada Sandstone White and salmon-red sandstone. Upper level-bedded Moab Member forms stair steps, lower mostly cross-bedded Slick Rock Member forms cliffs. 150 Entrada Point Moab, Utah Slick Rock, Colo. 195 Jurassic and Triassic(?) (missing) EROSIONAL UNCONFORMITY 210 Late Triassic(?) Kayenta Formation Red and purple siltstone and shale, and sandstone and conglomerate. Forms bench between two cliffs and mesas between canyons. 45-80 Kayenta, Ariz. Late Triassic Wingate Sandstone Buff and light red sandstone. Cross-bedded and level-bedded. Forms highest cliffs and most of named rock features in Monument. 350 Fort Wingate, New Mex. Chinle Formation Red siltstone and shale, and some limestone conglomerate. Forms steep slopes at foot of cliffs. 80-100 Chinle Valley N.E. Ariz. GREAT UNCONFORMITY 240-1000 Triassic, Paleozoic, Younger Proterozoic (missing) Unnamed Schist, gneiss, granite, and pegmatite dikes. Floors main canyons and forms high bluff above The Redlands. Unknown 1500 Older Proterozoic

After the materials of the sedimentary rocks were deposited and covered by younger layers, they generally became saturated or partly saturated with ground water containing small amounts of dissolved minerals. Some of these minerals precipitated from solution and cemented the loose particles into rocks of varying hardness. Thus, most of the sandstones are partly cemented with the mineral calcite, composed of calcium carbonate (CaCO₃), but some are cemented also with silica (SiO₂) or hematite (Fe₂O₃).

Look almost anywhere in the Monument and you will see that the rocks are piled up in layers of different color, thickness, and hardness—much like a vast layer cake. In most of the Monument, these layers are flat or slope gently down to the northeast, but along the northeastern boundary they are sharply bent or broken as though the cake had been carelessly placed over the edge of a table and had sagged.

Let us consider these layers one by one, beginning with the oldest at the bottom, for each is a partial record of events long past. Layers of rock that can be easily recognized and distinguished from other layers are called formations and are named after a place where they are well exposed. For the name to be accepted for general usage it must be the first published description in a technical report of a particular sequence of rock layers. The places after which the formations of the Monument were named are given in the rock column ([fig. 7]), and the outcrops of the formations are shown on the geologic map ([fig. 8]). In the pages that follow, the geologic events that shaped the Monument we see today are discussed in chronological order, beginning with the oldest rocks that floor the deep canyons.

GEOLOGIC MAP of Colorado National Monument and vicinity, simplified and greatly reduced from part of maps at scale 1:31,680 by Lohman (1963, 1965a). For additional surficial deposits in the Grand Valley and Orchard Mesa see Cashion (1973). (Fig. 8)
[High-resolution Map]