Monument Valley sits at the top of a wide anticline, the Monument Upwarp. The layers of sandstone, siltstone and shale were desposted and buried here millions of years ago, before the land gave way to uplifting and folding. The reddish hues in the sand and rock of the valley are due to iron oxide and the the black streaks which decorate the rock and known as desert varnish are manganese oxide. Eroded by wind and rain, soft red shale undermines the stronger sandstone, producing the many buttes and pinnacles. The buttes and pinnacles of Monument Valley date back 270 million years. Cedar Mesa Sandstone also make up the formations that are known the world around. The base of the mesas are usually composed of Halgaito shale. Volcanic activity occurred in areas surrounding the Uplift, releasing molten rock from underneath. Remnants of these volcanoes are scattered in the distance. Alhambra Rock is another igneous rock which protrudes above the surface north of Monument Pass.
There are very few trees in the area because of the extreme dryness and lack of moisture, but an occasional juniper will appear near the edges of the valley. Purple Sage is prominent in the area and brings contrast against the deep red earth colors. During the rainy season, Cliffrose, Rabbitbrush and Snakewood can be seen growing. With plantlife being sparce, there is less wildlife in the Monument than in other parts of the Colorado Plateau.