If all the rock strata in the park were present at one locality, their sequence and thickness would be those shown on the right-hand side of the graphic section in figure 9. However, because of the lateral changes in thickness and character and the wedging out of certain beds, such as the White Rim Sandstone Member of the Cutler Formation, no two sections of the strata are exactly alike. This will be brought out in photographs of different exposures of rocks in various parts of the park. An often-asked question is, why are most of the rocks so red? This can be answered by one word—iron, the same pigment used in rouge and in paint for barns and boxcars. Various oxides of iron, some including water, produce not only brick red but also pink, salmon, brown, buff, yellow, and even green or bluish green. This does not imply that the rocks could be considered as sources of iron ore, for the merest trace of iron, generally only 1 to 3 percent, is enough to produce even the darkest shades of red. The only rocks in the park that contain virtually no iron are white sandstones of the White Rim Sandstone Member of the Cutler Formation (figs. 21-24) and the Navajo Sandstone. [Illustration: Fig. 10, first section] [Illustration: SECTION ACROSS CANYONLANDS NATIONAL PARK from North Point at west (left), via Grand View Point in middle, to Needles Overlook at east (right), showing the three principal topographic levels and character of the rock strata. Line of section bends at Grand View Point, which is northernmost part. (Fig. 10)] As pointed out by Stokes (1970, p. 3), microscopic examination of the colored grains of quartz or other minerals shows the pigment to be merely a thin coating on and between white or colorless particles. Sand or silt weathered from such rocks soon loses its color by the scouring action of wind or water, so most of the sand dunes and sand bars are white or nearly so.