The volcanic history of Arizona spans more than one billion
years. There are seven volcanic fields which have erupted within
the last four million years. One of them entombs pottery of
local inhabitants of the time. One dammed the Colorado River in
the Grand Canyon several times. Another produces world-class
gemstones, and another is associated with the 1887 earthquake
which shook Southern Arizona and Northern Sonora. The map below,
from the Arizona Geological Survey shows the location of these
recent and older volcanic fields. This article discusses those
shown in red. For more information on rock names, see the
Igneous rock naming page to the left. Uinkaret Volcanic Field
(UI on the map) The Uinkaret volcanic field lies on the north
rim of the Grand Canyon in northwestern Arizona. Four major
eruptions of basalt from this field flowed into the Grand Canyon
and dammed the Colorado River between 725,000 and 475,000 years
ago, between 400,000 and 275,000 years ago, between 225,000 and
150,000 years ago, and bet