Figure 1T This chapter describes the unique features shown on this map. They reveal how the Grand Canyon formed catastrophically, several thousand years ago. Two former lakes, Grand Lake and Hopi Lake, are superimposed on today’s terrain, shown in nearly true color. The white oval encloses the high Kaibab Plateau, which extends slightly south of the Colorado River. The circle marks the north half of Marble Canyon, about a dozen barbed canyons, the funnel, and parts of Echo Cliffs and Vermilion Cliffs.  The dashed white line marks the boundary of the uplifted, roughly circular Colorado Plateau, also shown in the inset.

Grand Lake held a volume of water almost twice that of Lake Michigan. The volume of water in Hopi Lake was roughly that of Lake Huron.¹ To appreciate the size of Grand Lake, see Figure Figure 22 on page 246