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 Many
pueblo and cliff dweller ruins, with accompanying artifacts, indicate prehistoric occupation. The first sighting of the Grand Canyon by a
European is credited to the
Francisco Coronado
expedition of 1540, and subsequent discovery to two Spanish priests, Francisco Domínguez and
Silvestre Vélez de Escalante
, in 1776. In the early 1800s trappers examined it, and sundry government expeditions exploring and mapping the West began to record information
about the canyon. By the 1870s, following the exploration of
John Wesley Powell
and others, extensive reports on the geography, geology, botany, and ethnology of the area were being published.
 Briefly
summarized, the geologic history of the canyon strata is as follows. The crystallized, twisted, and contorted unstratified rocks of the inner
gorge at the bottom of the canyon are
Archaean
granite and
schist
about two billion years old. Overlying these very ancient rocks is a layer of Proterozoic
limestone
,
sandstone
and
shales
that are more than 500 million years old. On top of these are Palaeozoic rock strata composed of more limestone's, freshwater shales, and cemented
sandstones that form much of the canyon's walls and represent a depositional period stretching over 300 million years. Overlying these rocks in
the ordinary geologic record should be a thick sequence of Mesozoic rocks (245 to 66.4 million years old). Rocks dating from the
Mesozoic Era
in the Grand Canyon, however, have been entirely eroded away. These rocks are found, nonetheless, in nearby southern Utah, where they form
precipitous butte remnants and vermilion, white, and pink cliff terraces. Of relatively recent origin are overlying sheets of black lava and
volcanic cones that occur a few miles southeast of the canyon and in the western Grand Canyon proper, some estimated to have been active within
the past 1,000 years.
 The
cutting of the mile-deep Grand Canyon by the Colorado River is an event of relatively recent geologic history that began not more than six
million years ago, when the river began following its present course. The Colorado River's rapid velocity and large volume and the great amounts
of mud, sand, and gravel it carries swiftly downstream account for the incredible cutting capacity of the river. The
depth of the Grand Canyon is due to the cutting action of the river, but its great width is explained by rain, wind, temperature, and chemical
erosion, helped by the rapid wear of soft rocks, all of which steadily widened it.
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