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A father and daughter hike from the Colorado River at the canyon floor up to the rim, and each step up the rock layers is a step forward in geologic time. When the girl finds a fossil in a layer, the page opens into the ancient world that layer records, such as a shallow sea or a desert of sand dunes.
A canyon forms in three stages. First, sediments settle in seas, rivers and dunes and harden into layered rock over hundreds of millions of years.
Each rock layer is a snapshot of the environment present when it formed. Limestone with marine fossils means a shallow sea, and cross-bedded sandstone with reptile tracks means wind-blown dunes. Reading the stack from bottom to top turns a cliff face into a chronological history of changing seas, coastlines and deserts.
Along the way, desert cacti and heat-adapted animals give way to pinyon-juniper woodland and then to ponderosa pine forest. Elevation compresses latitude, so distinct ecosystems sit stacked in bands on a single hike.