as the snow thwarted our plan to hike down into the canyon, we opted to walk along the rim instead. starting near the Grand Canyon Village, the “Trail of Time” introduces visitors to the geological stages and rock formations that make up the Canyon. bronze markers embedded in the trail every meter indicate the passage of one million years of geologic time, from about 2 billion years BCE to the present and examples of various rock formations march along the side of the trail.
the oldest rocks of the Canyon lie more than 3,000 feet below the rim and aren’t visible from the rim. the Elves Chasm Gneiss is only found near the Elves Chasm and while its origins aren’t precisely known, some geologists suspect it was part of an old continental crust. the oldest rocks visible from the rim are the Vishnu basement rocks, which consist of ancient igneous and metamorphic rocks formed deep beneath the earth’s surface when island arcs (like those found off Asia today) collided with a continental mass. the Vishnu formations are primarily crystalline in structure — schist, gneiss, and granite — which differs significantly from the layers of Canyon above it, which are primarily sedimentary in composition.
the Grand Canyon Supergroup, layers of rock that have tilted, make up the next set of geological features of the Canyon. both sedimentary and volcanic in nature, the layers of the Supergroup formed over some 400 million years as continents separated and a new ocean basin formed in the new space between. precise dating for the Supergroup proves somewhat challenging; normally fossil records would aid in those determinations but these layers formed prior the diversification that resulted in hard skeletal structures of creatures.
above the Supergroup are a series of sedimentary layers collectively known as Layered Paleozoic Rocks. despite being lumped together, each layer illustrates unique characteristics that resulted in its formation — the presence of coastal sand dunes, the bottom of an ocean, etc. they show similar characteristics so some of the other National Parks found nearby and which are also part of the Colorado Plateau (Zion, Bryce, Arches, etc.) — an area of mostly flat-lying sedimentary rocks that were elevated thousands of feet above sea level some 70 million years ago (when the Rocky Mountains formed) and were then carved out by erosion. it’s easiest to see the effects of this erosion in these layers; each type of rock deteriorates in its own manner and the result is the recognizable stepped-pyramid look of the Canyon walls. shale erosion forms slopes; sandstone and limestone, cliffs; metamorphic, steep slopes as seen in the Vishnu basement rocks near the river.
the layer that forms the rim was the most recent set down. the Kaibab Formation formed in a shallow, warm sea about 270 million years ago — before dinosaurs roamed the earth. it covers a huge portion of the southwest, stretching from Northern Arizona into Utah, Nevada, and California.
the trail ends at the Yavapi Museum of Geology, originally dedicated as an observation point for studying geology in 1928. it now houses various interpretative exhibits, a topographical representation of the canyon, and binoculars to give people a chance to glimpse the river rushing along at the base of the Canyon. it was also rather sweltering, trying overly hard to keep the bright, sunny, 40-ish weather outside.